Abstract
Transcranial direct current stimulation (tDCS) has emerged as a widely accessible, noninvasive technique capable of modulating cortical excitability. A rapidly expanding body of sports-science literature suggests that it can produce modest but measurable gains in endurance, strength, skill acquisition, and perceived exertion. This editorial reviews the physiological mechanisms underlying tDCS, evaluates the evidence for its ergogenic effects, and situates the technology within the broader framework of “neurodoping”. Applying the 2021 World Anti-Doping Agency (WADA) Code, I argue that tDCS already satisfies 2 of the 3 criteria for prohibition – namely, potential performance enhancement and violation of the spirit of sport – while failing the 3rd criterion, as standard protocols pose minimal health risk. This editorial also considers practical and ethical counterarguments to a ban, including tDCS’s low cost, relative safety, requirement for continued training effort, and the near-impossibility of detection or enforcement. Drawing parallels with accepted performance aids such as mindfulness, nutrition and altitude tents, this editorial concludes that outright prohibition could drive use underground and impede open scientific scrutiny. Instead, it advocates rigorous long-term safety monitoring, transparent research, and nuanced policy development that distinguishes therapeutic from performance applications. Ultimately, it frames tDCS as a “still-legal” yet ethically contested innovation at the frontier of sports technology, urging stakeholders to balance principles of fair play with scientific evidence as the debate over neurodoping continues to evolve.
Key words: sport, transcranial direct current stimulation, tDCS, neurodoping
Introduction
Athletic activity is fundamental to maintaining health and serves as a source of recreation and competition across hundereds of sports. In most disciplines, victory or defeat is determined by individual points or fractions of a second. Athletic performance is influenced by multiple factors, including athletes’ physical and psychological characteristics, environmental conditions and potential distractions. Athletes, coaches and scientists must account for these influences to minimize negative effects and maximize potential benefits.
For decades, a great scientific race has been underway to identify methods with demonstrated efficacy in enhancing athletic performance. In this race, 3 paths can be distinguished in the search for performance enhancements. The 1st priority is the development of safe and effective methods that comply with the anti-doping rules established by the World Anti-Doping Agency (WADA). Such methods must uphold the principles of fair play and honest competition, ensure athlete safety and remain free of ethical or moral objections. Moreover, even when proven effective, they should be accessible to all.
The 2nd path involves developing methods that violate WADA rules but are not yet recognized by WADA as doping or cannot currently be detected. The 3rd and final path comprises methods that are or will be recognized as doping but for which reliable detection is problematic. This 3rd path carries a real risk of exposure and often leads to high-profile scandals, revocation of titles and exclusion of athletes from competition.
What is transcranial direct current stimulation?
Transcranial direct current stimulation (tDCS) is a noninvasive technique that delivers a weak, continuous electrical current to the brain through 2 or more saline-soaked sponge electrodes – typically 1 anode and 1 cathode – placed on the scalp.1 The procedure is painless, generally well tolerated and considered safe, with few reported side effects.2 A small, battery-powered stimulator generates a direct current, typically between 0.5 and 2 mA, a fraction of which penetrates the skull to reach cortical tissue. The polarity of the current determines its effect: Anodal stimulation generally depolarizes neurons and increases excitability, whereas cathodal stimulation hyperpolarizes neurons, reducing activity.3, 4 Current flows between the electrodes, making standard tDCS relatively diffuse; however, the use of smaller electrodes can enhance the focality of stimulation.5 Transcranial direct current stimulation sessions typically last 15–30 min, with 20-min protocols being most common. The physiological aftereffects outlast the stimulation: as little as 3 min can induce measurable changes, while 10 or more minutes at 1–2 mA can stabilize these changes for at least 1 h.4, 6 A single 15-min session can modulate cortical excitability for approx. 90 min, and repeated sessions can further extend these effects.7, 8, 9 Such aftereffects are thought to result from subthreshold membrane polarization and subsequent synaptic plasticity, rather than direct neuronal firing.10 Multiple studies have demonstrated that tDCS can induce long-lasting, long-term potentation (LTP)-like or long-term depression (LTF)-like plasticity in the cortex, resembling classic Hebbian learning mechanisms.11 This plasticity depends critically on NMDAR (N-methyl-D-aspartate receptor) signaling and modulatory factors such as brain-derived neurotrophic factor (BDNF). For example, pairing anodal polarization with low-frequency synaptic input can produce persistent LTP in rodent cortex, an effect abolished by NMDAR antagonists.8 Importantly, these mechanistic effects are highly context-dependent: The impact of tDCS interacts with the preexisting state of the cortex and the ongoing activity of targeted networks. Stimulation during rest compared to task performance, or even differences in arousal state or time of day, can reverse or attenuate the expected excitability changes – a phenomenon known as metaplasticity.12, 13 Moreover, tDCS does not act in isolation on a single brain region but instead modulates distributed networks. Brain-network models emphasize that perturbing 1 node (e.g., M1) can propagate effects across connected circuits.14 Empirical imaging studies confirm that tDCS alters large-scale functional connectivity, so behavioral outcomes depend on the broader network state.15, 16 In summary, the primary physiological signatures of tDCS – membrane polarization, shifts in excitation–inhibition balance and plasticity – are well established, but their expression varies with ongoing brain dynamics.
A critical perspective also acknowledges that brain stimulation operates within a body–brain milieu. Neuromodulation does not override the influence of autonomic, endocrine or emotional states. For example, emotional arousal induces autonomic responses, such as heart rate acceleration or deceleration, which in turn affect brain function.17 Fear and stress recruit prefrontal–limbic circuits that regulate both cortical excitability and learning.18, 19 Moreover, the same threatening stimulus can elicit different heart rate and brain responses depending on context – for instance, during anticipation or extinction training.20, 21 Hormonal factors such as cortisol also feedback on synaptic plasticity and memory networks.22, 23 In the sporting context, variables such as stress, fatigue, motivation, and metabolic state are likely to interact with any neuromodulatory intervention. These layers of brain–body–emotion interaction imply that even well-documented physiological effects of tDCS must be interpreted within a dynamic system. Simple cause–effect assumptions (e.g., tDCS → performance improvement) risk overlooking how internal states gate plasticity.
Finally, it is evident that individuals differ markedly in their neurophysiological responses to tDCS. Genetic polymorphisms, cortical anatomy, neurotransmitter levels, and prior experience can all influence sensitivity to stimulation.24, 25, 26 For example, studies of conditioned fear have shown that genetic variation can substantially modify autonomic responses, such as heart rate, to identical stimuli.27 By analogy, 2 athletes receiving the same tDCS protocol may experience very different neural effects. This baseline variability is often obscured in group-averaged data but contributes to failed replications and mixed outcomes. In practice, any ergogenic benefit of tDCS in sport will likely interact with an individual’s unique neurochemical and neuroplastic profile.
There are 3 areas of scientific interest for tDCS. The 1st is reducing the symptoms of neurological and psychiatric conditions. Transcranial direct current stimulation has been shown to reduce symptoms of depression,28 schizophrenia,29 addiction,30 anxiety disorders,31 neurodegenerative diseases,32 post-traumatic stress disorder (PTSD),31 neurodevelopmental disorders,33 epilepsy,34 and many other conditions. The 2nd area of application is the use of tDCS to improve cognitive function in healthy individuals. Transcranial direct current stimulation has been shown to improve working memory,35 associative memory,36 episodic memory,37 creativity,38 decision-making,39 inhibitory control,40 numerical cognition,41 foreign language learning,42 and many other domains related to human cognition. The 3rd, and most interesting, area is improving performance in sports. Numerous studies have shown that tDCS improves the psychophysical performance of athletes by increasing limb strength and endurance and reducing perceived exertion and fatigue. We will continue to a detailed discussion of the effects of tDCS on performance in athletes in the next section.
What is “neurodoping”?
Neurodoping, also referred to as brain doping or cognitive enhancement in sports, denotes the use of interventions aimed at improving an athlete’s mental or cognitive functions – such as focus, learning or decision-making – to enhance performance.43 It includes both pharmacological approaches, such as nootropic agents or psychostimulants (e.g., modafinil, methylphenidate (Ritalin), or Alzheimer’s medications like donepezil, memantine and rivastigmine), and non-pharmacological techniques involving direct brain stimulation (e.g., tDCS or transcranial magnetic stimulation (TMS)).44, 45 These interventions aim to enhance athletic performance by sharpening cognitive functions – such as concentration, alertness and strategic thinking – while also improving motor skills, endurance, motivation, and other psychological factors that contribute to success.44, 46 For example, stimulant “smart drugs” such as modafinil or methylphenidate (Ritalin) can increase alertness and reaction time, benefits thought to aid not only physical sports but also mind sports such as chess.44, 47 The rise of neurodoping, however, raises significant ethical concerns: Critics argue that artificially enhancing the brain confers an unfair advantage and undermines both fairness and the “spirit of sport” that underpins athletic competition.46 Debates also extend to the question of an athlete’s praiseworthiness when using such aids, raising doubts about whether achievements attained with cognitive enhancements are truly deserved – a discussion often framed in terms of moral desert, that is, whether neurodoping diminishes an athletes praiseworthiness or prizeworthiness.44 From a regulatory perspective, neurodoping currently occupies a grey area: WADA has not yet explicitly banned most neurodoping methods. Under existing definitions of doping, which apply only to substances and methods on the Prohibited List, these brain-enhancing techniques remain legal in sport for now.45, 48 The absence of prohibition has sparked active debate among experts and policymakers. Some have urged WADA to ban neurostimulation techniques such as tDCS, arguing that they fulfill the criteria for doping and threaten both sporting integrity and athlete safety.46 Others, however, advocate more permissive approaches, suggesting that safe and accessible neuroenhancement could even help level the playing field. Proponents note that, unlike steroids or other traditional forms of doping – which can boost performance without effort – techniques like tDCS still require athletes to train rigorously to obtain benefits, potentially making them a fairer form of enhancement.49 Real-world instances of neurodoping have already been observed, which further fuels this debate. For example, some Olympic athletes and professional sports teams have reportedly experimented with tDCS during training in hopes of gaining a competitive edge.47 Additionally, in competitive chess (a sport with anti-doping rules), studies have found that cognitive stimulants such as modafinil or Ritalin can significantly improve a player’s performance, showing that even mind sports are subject to neurodoping considerations.47 Finally, there are clear risks and side effects associated with neurodoping: Athletes who use neural enhancement without medical supervision risk adverse effects such as dermatological lesions or burns from improper electrode use in brain stimulation (e.g., tDCS devices can cause scalp burns if used incorrectly), and the off-label use of psychoactive “brain booster” drugs (for example, rivastigmine patches) has been linked to skin rashes and other health issues.45
Transcranial direct current stimulation in sports: Hit or miss?
Much research effort has been devoted to demonstrating the effectiveness of tDCS in improving athletic performance. Numerous review studies have shown that tDCS improves running and cycling performance,50 endurance and maximal force production,51 upper-limb motor and endurance performance,52, 53 exercise performance,54 maximal strength and lower limb explosive strength,42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55 performance in basketball players,56 physical and psychological performance in national- or international-level athletes,57 and visuomotor performance,58 as well as lowers ratings of perceived exertion.59 Across sport tasks, recent meta-analyses suggest small average ergogenic effects, with important differences by outcome and protocol. A 2022 synthesis of 43 studies reported an overall standardized mean difference (SMD) of 0.25 (95% confidence interval (95% CI): 0.14–0.36), with strength (SMD = 0.31) and visuomotor tasks (SMD = 0.29) tending higher than endurance (SMD = 0.18). However, effects were inconsistent across studies, meta-regressions did not isolate robust stimulation parameters, and authors cautioned that factors like genetics, sex and training history likely moderate responsiveness.58 Other review concluded that any positive impact on exercise outcomes is small and potentially inflated by low study quality and selective reporting.60 The sport-performance evidence is mixed and methodologically heterogeneous. While multiple trials report improvements, synthesis across studies yields small average effects and substantial between-study variability, with suspected publication bias. Many experiments are small and underpowered, and responses vary widely between individuals, with only ~39–45% showing the expected excitability or behavioral change in classic motor-cortex paradigms. These features, together with blinding/sham limitations (standard sham can be biologically active and participants often guess condition above chance), argue for a cautious interpretation of apparent benefits.26, 61, 62, 63
Even a cursory examination of the scientific literature on tDCS suggests 2 conclusions. First, tDCS is being intensively studied in the context of sports. Thousands of studies have already been published in this area. This demonstrates the scientific interest in tDCS, which is good, as our understanding of the brain mechanisms of tDCS is still limited. However, to date, more is known about the mechanisms of tDCS in alleviating the symptoms of various diseases. Meanwhile, the mechanisms of tDCS in improving athletic performance are enigmatic.64 In other words, tDCS has shown performance benefits in some cases, but we still do not fully understand how or why these occur. The 2nd conclusion follows from the 1st: Since so many experiments have been conducted using tDCS in sports, can we speak of a new era of “neurodoping” in sports? If researchers are intensively studying the use of tDCS in sports, should we suspect that tDCS has already been implemented in training and athletic preparation and is being used as a “secret weapon”? Transcranial direct current stimulation use is virtually undetectable. The only telltale signs of tDCS use are a slight redness of the scalp where the electrode was attached, but this redness is not always present and disappears very quickly.
Evaluating tDCS under the 2021 WADA doping criteria
The 2021 WADA Code sets out 3 criteria for determining whether a substance or method should be considered doping. A substance or method may be added to the Prohibited List if it meets any 2 of these 3 criteria: 1) medical or scientific evidence that it has the potential to enhance, or actually enhances, sport performance; 2) evidence that its use presents an actual or potential health risk to the athlete; and 3) WADAs determination that its use violates the spirit of sport. In this section, we analyze tDCS against each criterion, considering both athletic use (i.e., performance enhancement in healthy athletes) and clinical or therapeutic use (i.e., medical treatment), with reference to established knowledge about tDCS and the 2021 WADA Code.
Criterion 1: Potential to enhance sport performance
WADA’s first criterion considers whether there is scientific or medical evidence that tDCS “has the potential to enhance, or actually enhances, sport performance.” Here, we evaluate the performance-enhancing potential of tDCS in the context of athletic competition, as distinct from its application in clinical therapy.
Athletic use of tDCS: Performance enhancement potential
Transcranial direct current stimulation is an experimental, noninvasive brain stimulation technique that modulates cortical excitability and has the potential to improve certain cognitive and motor functions. As a tool for neuroenhancement, it has been applied to healthy individuals to improve motor control and learning, including in athletic contexts. For instance, studies have demonstrated that tDCS can enhance motor skill acquisition and cognitive performance in healthy volunteers, effects that may translate into gains in athletic performance. Emerging evidence suggests that stimulating specific brain regions with tDCS may acutely improve motor skills or delay fatigue, while repeated sessions can accelerate longer-term skill acquisition. Notably, reports indicate that some elite athletes have already experimented with tDCS during training in an effort to gain a competitive advantage.
It must be emphasized, however, that scientific findings on the ergogenic effects of tDCS are mixed. Although individual studies have reported improvements in endurance, reaction time and skill learning, recent meta-analyses highlight inconsistent results and considerable methodological variability.65 The precise neurophysiological mechanisms by which tDCS might enhance performance remain unclear, and several well-controlled trials have found minimal or no benefit. Nonetheless, WADA’s threshold of “potential to enhance” does not require conclusive or consistent evidence of enhancement. The mere existence of plausible performance gains, supported by some scientific evidence, is sufficient to satisfy this criterion. By WADA’s standards – which require only the potential for enhancement, not consistent proof – tDCS meets Criterion 1. It artificially modulates brain circuits in ways not achievable through conventional training, thereby offering athletes a possible edge. Thus, although its effects may be modest and continued training remains necessary, the potential for direct performance enhancement through brain stimulation fulfills the performance-enhancement criterion.
Clinical/therapeutic use of tDCS: Performance effects
In clinical and therapeutic contexts, the primary aim of tDCS is to restore or normalize function rather than to enhance performance beyond natural baselines. It has shown promise in treating neurological and psychiatric conditions, including motor recovery after stroke, relief of depression or chronic pain, and mitigation of cognitive decline. In such cases, any observed “performance” improvements – such as better memory in Alzheimer’s disease or improved mobility in Parkinson’s disease – represent medical benefits rather than competitive sport enhancements. Current evidence highlights tDCS as a valuable therapeutic tool for difficult-to-treat disorders and symptoms. Its use to help patients regain normal function or quality of life is not intended to confer a supernormal athletic advantage, but rather to counteract illness. Accordingly, in the therapeutic context, the effects of tDCS would not be classified as “performance enhancement” in the sporting sense; they represent rehabilitation. If an athlete were to use tDCS under medical supervision to treat a clinical condition – e.g., to manage depression or pain – this would constitute legitimate medical use. WADA provides for Therapeutic Use Exemptions (TUEs), which permit necessary treatments even when they involve otherwise prohibited methods. In short, clinical applications of tDCS are not intended to enhance sport performance, and any improvements are incidental to treating a health condition. Accordingly, therapeutic use of tDCS does not satisfy Criterion 1, except insofar as it may incidentally restore an athlete to their baseline capabilities.
Criterion 2: Actual or potential health risk to the athlete
The 2nd criterion concerns whether tDCS poses an “actual or potential health risk” to the user. In this section, we evaluate the safety profile of tDCS and its associated risks, distinguishing between potential misuse in athletic contexts and controlled clinical applications.
Athletic use of tDCS: Health risks and safety
A key consideration for Criterion 2 is the excellent safety profile of tDCS when protocols are properly followed. According to broad consensus among researchers and clinicians, there is “no evidence for a serious adverse event being caused by tDCS” in human trials.66, 67, 68 Typically, tDCS delivers a weak current of 1–2 mA to the scalp for a limited duration, and decades of cumulative research have not identified lasting injuries under these conditions. Reviews of clinical trials report no unexpected or serious adverse events across hundreds of participants, including vulnerable groups such as older adults. Importantly, even in individuals with epilepsy – where brain stimulation might raise particular concern – no seizures or exacerbation of epileptic activity have been causally linked to tDCS in clinical studies.
The side effects of tDCS are typically mild, transient and localized. Common minor reactions include scalp itching, tingling, a burning sensation, or mild headache during or shortly after stimulation. These symptoms generally resolve quickly and have not been linked to lasting harm. Even in trials involving repeated sessions – for example, daily stimulation over several weeks – participants have tolerated the procedure well, with no cumulative adverse effects reported. This favorable safety record reflects both the low intensity of currents used and the careful exclusion of individuals with contraindications in research settings.
However, one must consider the “potential” health risks, including those arising from misuse. While tDCS itself, as used in published studies, appears safe, improper use could introduce dangers. Experts caution that if tDCS is performed incorrectly or without proper medical guidance, serious injuries are possible. For example, using electrodes over broken skin or wounds on the scalp can cause burns or skin lesions. Likewise, individuals with metal implants in the head (aneurysm clips, deep brain stimulators, cochlear implants, etc.) could be at risk – applying current near metal can concentrate current and potentially lead to tissue damage or even life-threatening outcomes. These scenarios underscore that unsupervised, amateur “do-it-yourself” (DIY) tDCS (which has emerged in some communities) carries non-negligible risks. If athletes were to self-administer excessive stimulation in pursuit of performance gains, they might exceed established safety limits, possibly causing unknown long-term neural changes or acute injuries. Additionally, there is a theoretical concern that enhancing one brain function might impair another (a trade-off), as 1 study noted tDCS improving numerical skills at the expense of another cognitive ability. Such off-target or long-term effects remain under investigation.
Overall, in the athletic context, tDCS does not inherently represent a significant health risk when used within recommended parameters, as no direct evidence of harm has emerged from controlled studies. The routine practice of testing tDCS on healthy volunteers (even for multi-week protocols) without incident attests to its general safety. However, the absence of documented harm so far does not guarantee that tDCS is without health risks. WADA’s Criterion 2 concerns potential as well as actual harm. We do not yet know the long-term consequences of repeated brain stimulation: Chronic use of tDCS could lead to unforeseen neural changes or side effects. For example, 1 study found that tDCS improved one cognitive skill while impairing another, hinting at complex trade-offs in brain function. Moreover, unsupervised or improper use (the so-called “DIY” tDCS trend) can introduce real dangers: users might over-stimulate, place electrodes incorrectly or ignore contraindications, potentially causing burns, tissue damage or unpredictable neural effects. Because these long-term and misuse-related risks are not fully understood, tDCS could be seen as posing a potential health risk. In summary, while short-term use appears safe, the unknown long-term and misapplication hazards mean Criterion 2 cannot be dismissed; there is at least a potential health risk that meets WADA’s wording for this criterion.
Clinical and therapeutic use of tDCS: Health risk considerations
From a clinical perspective, the safety of tDCS is a paramount concern, and the literature gives a reassuring picture. In therapeutic trials, patients (including those who are elderly or have neurological disease) have undergone tDCS with very few adverse events. For instance, a review of 19 studies involving over 500 older adult patients reported no serious adverse events and no major safety issues attributable to tDCS.68 Minor side effects in patient populations mirror those in healthy subjects – transient scalp discomfort or fatigue, which do not require medical intervention. In conditions like depression, stroke and chronic pain, tDCS has been delivered in repeated sessions with a strong safety record. One favourable reason tDCS is being explored as an alternative to pharmaceuticals is because it lacks the systemic side effects that many drugs have.
Clinically, one must still be cautious. Medical teams employing tDCS adhere to strict protocols to avoid risks (screening for implants, monitoring skin condition, using proper electrode preparations, etc.). In the hands of clinicians or researchers, tDCS is handled as a medical device with appropriate oversight. Under these conditions, tDCS does not pose a significant health risk to patients. On the contrary, it is often sought for patients precisely because it has a benign side-effect profile compared to medications (e.g., treating depression with tDCS to avoid the side effects of antidepressant drugs). Therefore, in the therapeutic use case, tDCS clearly fails to meet the “health risk” doping criterion. It is considered a safe treatment modality.
It is worth noting that if WADA were to ban tDCS as a doping method, athletes who genuinely need it for medical reasons could apply for TUEs to continue treatment. Such an exemption process underscores the difference between risk-laden abuse of a method by healthy athletes and legitimate medical use by those in need. In summary, tDCS is characterized by an absence of significant health risks in both healthy and clinical populations (aside from manageable minor effects), especially when compared to many pharmacological doping agents. Thus, it does not satisfy Criterion 2 under clinical-based use conditions. This form of intervention could help athletes suffering from injuries or neurological and psychiatric conditions recover faster.
Criterion 3: Violation of the “spirit of sport”
The 3rd criterion is more qualitative: It asks whether the use of tDCS is “against the spirit of sport”, as defined by WADA’s ethical principles. The spirit of sport is outlined in the Code’s introduction as “the ethical pursuit of human excellence through the dedicated perfection of each athlete’s natural talents”. It encompasses values like health, fair play, honesty, respect for rules, and fairness on a level playing field. Doping is deemed fundamentally contrary to the spirit of sport because it undermines these values – it allows success to be achieved through artificial aid rather than natural talent and hard work. We consider whether using tDCS for performance enhancement would violate these principles, and contrast that with its use in a therapeutic context.
Athletic use of tDCS: Ethical and fairness issues
Using tDCS as a performance enhancer in sport raises significant ethical and fairness concerns, directly engaging WADA’s “spirit of sport” criterion. Sport has traditionally celebrated achievements derived from athletes’ natural abilities, refined through training, practice and dedication. If competitors turn to electrical brain stimulation to gain an advantage, that edge is exogenous to their innate talent and training regimen, resembling the use of drugs or other artificial aids. In this sense, ergogenic use of tDCS may be regarded as a form of “neurodoping” – an external technical shortcut to improved performance. This clearly conflicts with the ethos of fair play and equal conditions. Athletes who do not use such technology would be at a disadvantage compared to those who do, creating an imbalance based not on skill or effort but on access to enhancement devices. This scenario is analogous to other banned methods of enhancement; indeed, researchers have explicitly begun calling on WADA to address “neurodoping” techniques like tDCS to preserve fair competition. If one athlete’s endurance or reaction time is artificially boosted by a brain stimulation device, the competition is no longer solely a measure of natural training and talent – it has introduced a technological arms race, which undermines the integrity of sport.
Moreover, the spirit of sport also encompasses athletes’ health and the natural enjoyment of sport. One might argue that even if tDCS is relatively safe, encouraging athletes to use any intervention on their brain for a competitive benefit puts psychological pressure on them to “keep up” with others, eroding the purity of sport. Respect for the rules and self-respect are also listed values – covertly zapping one’s brain to win, especially if it were prohibited, would violate these principles. In essence, using tDCS to enhance performance violates the spirit of sport for the same core reasons as using a chemical stimulant or blood doping: It is an artificial enhancer granting an unearned advantage and compromising the ideal of sport as a test of natural human ability and honest effort.
It is interesting to note that some ethicists have debated whether certain forms of enhancement might be acceptable in the future (for instance, caffeine was once monitored by WADA but is now permitted in moderation). In the Practical Guide book, the authors discuss that “the simple act of neuroenhancement itself is not unethical, as it represents a fundamental component of human life and development” – people regularly seek to improve themselves (through education, caffeine, etc.). They argue that tDCS use “in and of itself” is not inherently immoral. However, context is crucial: The same source immediately cautions that using tDCS without understanding its long-term consequences is ethically questionable. In sport, even if one viewed tDCS as akin to intense training or a nutritional supplement, the counterargument is that it directly alters brain function in a way not achieved by natural means, pushing the athlete beyond their innate limits. Until proven otherwise, this is closer to cheating than to innovation. The neuroethics literature broadly agrees that current neurostimulation devices, if effective as enhancers, would contravene the unwritten contract of sport – much like mechanical doping (e.g., hidden motors in bicycles) or gene doping. From an athletic standpoint, therefore, the use of tDCS for performance enhancement satisfies WADA’s “spirit of sport” violation criterion, as it conflicts with the principle of fair and natural competition. That said, the analysis is not without nuance.
If tDCS were truly safe with only modest effects, some argue that banning it while permitting other advanced aids is inconsistent. Later I point out that current WADA practice tolerates many enhancement-like strategies (mindset training, optimized equipment, etc.). Ethicists have suggested treating tDCS more like these – as part of science-backed training – until it clearly violates fairness. Likewise, Møller and Christiansen caution that the “neurodoping” scare is largely speculative; given tDCS’s mild effects and non-toxicity, a blanket ban might be premature.48
Other scholars emphasize that enduring physical effort is central to sport’s value. Erler argued that bypassing “inner challenges” via neuroenhancement could erode the character-building aspect of competition. He concluded there is at least reason to prohibit tDCS in endurance sports to preserve the role of effort and struggle.69 In his view, even a safe, accessible enhancer might still diminish what it means to achieve victory.
Ultimately, many conclude that tDCS’s ethical status depends on context. Used medically (to restore health) it upholds sport’s values; used for unfair gain it violates them. The debate shows tDCS is not simply “ethical” or “unethical” in all cases. Instead, factors like intent, outcome size and accessibility matter. This complicates a binary view: If tDCS modestly augments training and is equally available, some argue it could fit within a broad interpretation of the spirit of sport.70 Conversely, if it provides a large, exclusive boost, most agree it offends the ideals of fair competition.48
In summary, neuroethicists urge a balanced perspective: tDCS sits on a spectrum, and its ethical profile shifts with the circumstances of use. These analyses suggest WADA’s “spirit” criterion should be applied with nuance, recognizing that safe, equitable applications of tDCS might align with sport’s health and training values, whereas more secretive or unequal use would violate its core principles.
Clinical/therapeutic use of tDCS: Spirit of sport perspective
When tDCS is used therapeutically by an athlete (under medical supervision for a diagnosed condition), the ethical interpretation shifts. In this scenario, the athlete’s intent is not to “boost” performance above normal, but to recover health or function. This is akin to an athlete taking prescribed insulin for diabetes or using a rehabilitation technology after injury. Such use aligns with the spirit of sport insofar as it supports the athlete’s health – one of the core values listed by WADA – and helps them compete on normal rather than enhanced terms. The WADA Code explicitly recognizes this distinction through the TUEs process, which upholds the spirit of sport by allowing necessary medical treatments while still forbidding abuse of those treatments for performance gain. If an athlete with clinical depression uses tDCS under a doctor’s care to alleviate their symptoms, this could be viewed as ethical and within the spirit of sport, provided it simply brings the athlete back to their natural baseline. The spirit of sport concept includes values like “health” and “respect for self” – obtaining proper treatment honors those values.
Thus, therapeutic tDCS use does not violate the spirit of sport, whereas non-medical performance use does. The key factor is intent and effect: using technology to level the playing field (by restoring health) vs to tilt the playing field (by gaining an advantage). WADA’s stance is that doping is contrary to sport’s spirit because it’s an unfair shortcut. A medical intervention under a TUE is not considered a shortcut but rather a legitimate support for an athlete’s wellbeing. It’s analogous to the ethical difference between taking an anabolic steroid to build extra muscle (doping) compared to taking prescribed cortisone to treat severe inflammation (medicine).
Neuroethicists stress that therapy and enhancement lie on a continuum, not a strict binary. Shook et al. warned that drawing the line “where therapy ends” and enhancement begins is a mistake – enhancement effects can emerge even during ostensibly therapeutic use.71 In practice, tDCS used to restore an athlete’s lost function (e.g. treating depression or injury) is ethically akin to medicine – it “helps them compete on normal terms rather than enhanced terms”. WADA embodies this distinction via TUE: Treating a medical condition with tDCS (thereby returning an athlete to baseline) is compatible with the spirit of sport, whereas using the same technology explicitly to boost performance beyond natural abilities is not. As I noted, using tDCS like an insulin shot or rehab is aligned with sports values of health and respect, whereas using technology to level the playing field (by restoring health) vs to tilt it (by gaining an advantage) is the key ethical difference. When tDCS is applied under medical supervision for a diagnosed condition, its effects are restorative. This aligns with WADA’s values of health and fairness. The WADA Code explicitly allows necessary medical treatments (via TUE), recognizing that returning an athlete to normal capabilities does not gain an “unnatural” edge.
Some ethicists argue that certain enhancements could be permissible under fair conditions. A recent review emphasizes that any discussion of enhancement must tackle equitable access: If only the wealthy can use an ergogenic technology, it will worsen social disparities and violate justice.70 Ploesser et al. concluded that ethical approval of brain-enhancing methods hinges on ensuring they are safe, effective and widely available.70 In sports, however, perfect equity is elusive. Critics point out that athletes already benefit from high-tech gear and coaching to which poorer competitors have less access. As Kayser et al. note, even commonplace equipment (e.g. specialized bikes, prosthetics, swimsuits) is not equally available to all athletes, calling into question simplistic “everyone plays fair” arguments.72
Does tDCS meet WADA’s doping criteria?
Bringing the analysis together, a clear contrast emerges between the role of tDCS as a performance aid and its role as a therapeutic intervention.
A. Potential to enhance sport performance: tDCS has been shown to have the potential to improve various aspects of performance (motor learning, endurance, cognitive function). Even though training and effort are still required, these improvements come from artificially modulating brain activity. In other words, tDCS can provide an unnatural advantage by boosting an athlete’s own capacities beyond what natural training alone can achieve. Under WADA’s 1st criterion, even this potential for enhanced performance (via external brain stimulation) is sufficient to satisfy the performance-enhancement requirement.
B. Health risk to athletes: No. The use of tDCS does not represent an appreciable health risk based on current evidence. It has an excellent safety record with only minor side effects and no serious adverse events reported. While any misuse or unknown long-term effects warrant caution, tDCS is far safer than virtually all traditional doping substances. It fails to meet WADA’s risk criterion 4.3.1.2 in the sense that it does not pose a significant actual or potential harm to athletes under normal use.
C. Violation of spirit of sport: tDCS use for performance enhancement is at odds with the spirit of sport (in athletic use) – it compromises fairness, equality and the natural talent narrative of athletic competition. This satisfies WADA’s criterion 4.3.1.3 for prohibition. However, genuine medical use of tDCS (with no intent to unfairly enhance performance) would not violate the spirit of sport and is ethically acceptable, analogous to other medical treatments.
According to the Code, meeting any 2 of the 3 criteria is enough for WADA to prohibit a method. In the case of tDCS, Criteria 1 and 3 are fulfilled in the scenario of athletic performance enhancement, whereas Criterion 2 is not. Two out of 3 criteria being met suggests that tDCS could be considered for inclusion on the Prohibited List if WADA chooses. Indeed, some scholars have argued that tDCS already meets the necessary criteria and have urged WADA to act. On the other hand, the fact that tDCS poses minimal health risk and has unproven efficacy might weigh in the balance of WADA’s policy decision. WADA has thus far (as of the 2021 Code) not banned tDCS or other neurostimulation methods; this may reflect the still-emerging evidence and practical considerations about enforceability and medical use. In a recent neuroethics analysis, experts concluded that while tDCS likely satisfies WADA’s technical criteria for doping, it may be more prudent to monitor the technology rather than outright prohibit it at this stage.
Arguments against banning tDCS in sport
Unlike conventional training aids, tDCS works by directly altering brain function through electrical stimulation. Other legal methods (such as sports psychology, mindfulness, virtual reality (VR), neurofeedback, nutrition, or strength training) work indirectly – they rely on the body’s natural physiological and psychological adaptation to practice or diet.73, 74, 75, 76, 77, 78, 79, 80 In contrast, tDCS applies an external current to the scalp, artificially modulating neural circuits. This fundamental difference means tDCS is not simply another version of meditation or altitude training. It actively pushes the athlete’s brain beyond its innate limits, rather than harnessing normal adaptation. This artificial intervention makes tDCS distinct from accepted aids: It introduces a technological shortcut that those other methods do not. Even if tDCS were cheap and widely available, the issue of fairness is not resolved by price alone. The key point is that tDCS artificially alters the brain in a way that other methods do not. Simply making it accessible does not change the fact that it provides an external enhancement. Fair competition requires measuring athletes by their own unenhanced abilities and effort; any method that gives one athlete an artificial boost – even if it’s affordable – undermines this principle. In short, tDCS’s affordability or accessibility does not remove the ethical concern of its artificial advantage.
Third, we must revisit the “spirit of sport”. As outlined under WADA’s 3rd criterion, the use of tDCS for performance enhancement only weakly challenges this principle. Although neurostimulation may appear to offer an artificial shortcut, it in fact requires sustained training and produces, at best, modest gains – comparable to those achieved with other accepted high-tech training aids. In short, when used transparently, tDCS does not fundamentally undermine the values of dedication and fair play.
In light of tDCS’s excellent safety profile, its moderate and inconsistent performance benefits, and the practical difficulty of policing its use, there is currently little justification for banning it outright. Unlike potent doping agents, tDCS does not dramatically alter competition or endanger athletes’ health. Banning it prematurely could even be counterproductive – an unenforceable ban may drive covert use and create more unfairness. A more sensible approach is to continue monitoring and researching tDCS in sport rather than imposing a hasty prohibition despite the unsettled science.
Moreover, the performance benefits of tDCS, while demonstrated in some studies, are not overwhelmingly potent or reliable – calling into question whether it even provides an undue advantage. Scientific reviews and meta-analyses indicate that tDCS’s ergogenic effects are modest and inconsistent overall. For example, a meta-analysis of 36 studies found only a small average improvement in outcomes like exercise endurance, an effect that may be inflated by publication bias and methodological factors. Other analyses have concluded that tDCS has little to no significant impact on muscular strength or perceived exertion in exercise, with some positive findings hinging on isolated studies. While ongoing research continues to refine how, where and for whom tDCS might be most effective, it is clear that tDCS is not a guaranteed performance booster – many individuals experience no measurable benefit, and responders might gain only a marginal edge (e.g., a few percent improvement in a specific task). Such gains are comparable to those attainable through perfectly legal means like optimized nutrition (consider the small but crucial effects of carbohydrate loading or creatine supplementation) or psychological techniques. Critically, there is also high inter-individual variability in response to tDCS. Factors like neuroanatomy and genetics appear to make some athletes “non-responders” who get no boost at all from the same stimulation that aids others. This variability further blunts any blanket advantage – at the population level, tDCS is far from a surefire or unfair enhancement. Sports already tolerate many performance differences arising from genetics or variable responses to training; the uneven efficacy of tDCS is no different. In short, the current evidence paints tDCS as a low-risk, moderate-reward intervention. It does not dramatically distort competition outcomes in the way that potent doping agents can, which is likely why WADA has so far held off on prohibition pending more conclusive data. Given this evidence, a preeemptive ban would be scientifically premature, especially when less effective or comparably marginal aids (with far greater uncertainty of benefit) are not banned. A more sensible approach is continuing to study and monitor tDCS use in sport, rather than outlawing it despite the unsettled science.
Even for those who remain ethically uneasy about neurostimulation in sport, an outright ban on tDCS would pose severe practical challenges. Unlike pharmacological agents, tDCS leaves no trace in blood or urine, making enforcement of any prohibition extremely difficult. Anti-doping authorities would have no reliable test to catch an athlete who used tDCS during training or prior to competition. Policing a tDCS ban could only be done by witness reports or catching an athlete with a device in hand, an approach that is neither systematic nor fair. This raises the specter of uneven enforcement and the potential for covert use: If a method is easily hidden and undetectable, a ban may simply drive its use underground, favoring those willing to break the rules. That outcome – clandestine neurostimulation by some athletes while rule-abiding ones abstain – would undermine the very fairness and integrity that doping rules intend to protect. The history of altitude simulation illustrates this point. WADA considered banning hypoxic altitude tents on “spirit of sport” grounds, as they mimic high-altitude training artificially, but ultimately chose not to ban them in part due to enforceability and fairness concerns. It was recognized that prohibiting altitude tents would not only be hard to police but would also reward athletes who live or train at high elevations while penalizing those who tried to legally simulate those conditions. A similar logic applies to tDCS: Banning it could generate new inequities, favoring athletes who either use it covertly or who possess equivalent innate advantages. Moreover, effective regulation would be nearly impossible without intrusive surveillance. In contrast, allowing tDCS keeps the playing field transparent and subject to open scientific oversight. If it remains legal, athletes and coaches can discuss and publish their experiences with tDCS, and researchers can openly collaborate with teams to optimize safe use – all of which contributes to a better understanding of its true effects. This transparency is lost under a ban. It is telling that WADA has thus far opted not to list tDCS or other noninvasive brain stimulation methods as prohibited, despite tDCS seemingly fulfilling 2 of the 3 formal doping criteria. The likely reasons are the ones outlined above: Minimal health risk, still-emerging evidence of efficacy and serious doubts about enforceability. In a recent neuroethics analysis, experts concluded that while tDCS technically meets the criteria, the prudent course is to monitor the technology rather than ban it at this stage. This approach mirrors how WADA handles certain borderline substances (like caffeine, now on the monitoring program but not banned) and innovative training tools – proceeding with caution, gathering data, but stopping short of prohibition unless a clear threat materializes.
On balance, the ethical, scientific and practical arguments weigh strongly against banning tDCS in sport. It can be likened to other permitted performance aids that support training or mental preparation without undermining the core values of competition. Transcranial direct current stimulation is safe, with no appreciable risk to athlete health. Its effects are moderate and variable, offering no guarantee of victory and leaving the essential nature of competition intact. It is also accessible and relatively affordable, preserving fairness as long as it is equally available to all. Finally, it continues to require hard work from athletes, aligning with the spirit of sport’s emphasis on effort and dedication. Where concerns do exist (e.g., about fairness or future misuse), they are better addressed through regulation, education and ongoing research rather than an outright ban. Parallels can be drawn to advancements like nutritional science or sports psychology, which were once novel but are now integral to athlete preparation. Embracing tDCS as a legitimate tool encourages transparency and further study into its benefits and limits, ultimately helping sports authorities make evidence-based decisions. In contrast, a ban would be premature and unenforceable, potentially stifling research and driving use into the shadows. In summary, while tDCS does satisfy 2 of WADA’s doping criteria (enhancement potential and a surface-level departure from “natural” performance), those concerns are mitigated by its safety, equity of access and requirement for genuine athletic effort. Just as other enhancement technologies have been allowed to coexist with the ethos of sport, tDCS can be accommodated within athletics without undermining integrity or fairness.
Risk of abuse and injury
The human body has natural limits to its physiological capabilities. We experience fatigue, which signals that we should stop exercising and rest. We feel muscle pain, which signals that we should stop activity and investigate the cause, as damage may have occurred. These signals warn us that we have exceeded a critical point in our capabilities. By ignoring them, we expose ourselves to the risk of injury or even life-threatening situations. In the previous sections, I outlined evidence that tDCS can enhance physical performance in various domains (usually to a small degree). An important question that cannot be ignored is whether raising the threshold of our natural limits beyond safe levels is completely safe. If our bodies have limits: Can pushing them beyond physiological limits result in injury or even life-threatening situations? Unfortunately, there is no research on the long-term effects of tDCS on improving athletic performance. It is unknown whether athletes who regularly use tDCS and achieve better results are exposed to these new risks. There is therefore an urgent need to monitor the long-term effects of tDCS used to enhance athletic performance, and above all, its safety. Such action is necessary, of course, to refute these suspicions, but also to avoid providing arguments to anti-doping organizations that tDCS is a dangerous technique and should be banned.
Across thousands of sessions in clinical and healthy cohorts, conventional-parameter tDCS (typically ≤2–4 mA for ≤20–30 min) shows a strong safety record: Serious adverse events are not established and the most common effects are mild, transient sensations (itching, tingling, erythema) that also occur with sham; importantly, systematic reviews of repeated-session studies likewise do not show risk escalation within tested ranges.81 Nevertheless, these data come largely from short-to-medium-term protocols under supervision, not from chronic, performance-oriented use by healthy athletes, so caution is warranted when generalizing. The gap between laboratory protocols and season-long training cycles justifies explicit monitoring.
Several specific unknowns merit attention. First, domain-specific cognitive trade-offs have been documented: Stimulation that facilitates one aspect of learning can impair automaticity or slow responses in other domains or subgroups,82, 83 implying that a gain in a targeted skill (e.g., vigilance under fatigue) could be counterbalanced by decrements in decision speed, response inhibition or multitasking – capacities central to sport performance. These findings argue for assessing off-target cognition during long-term use.
Second, dose–response non-linearities and metaplasticity raise the possibility of subtle maladaptive plasticity with repeated tDCS sessions. Motor cortex studies demonstrate that increasing current intensity can invert expected polarity effects – e.g., cathodal stimulation at 2 mA may enhance rather than suppress excitability – and that session spacing can reverse or prolong aftereffects via homeostatic mechanisms.84, 85, 86 Over longer timescales, athlete-style protocols that cluster stimulation around training may therefore bias neural networks in unanticipated directions unless carefully monitored and adjusted.
Third, although rare and primarily reported in clinical samples, affective switches (hypo/mania) highlight that mood/arousal networks are susceptible to neuromodulation.87 Athletes operate under fluctuating sleep, travel stress, stimulants, and supplements – all probable modulators of state-dependent responses – so mood and sleep should be part of surveillance even in healthy users.
Fourth, dermatologic injury remains a practical concern in cumulative or unsupervised use. Case reports describe electrode-site burns resulting from poor contact, dried sponges, high impedance, or excessively prolonged sessions, while systematic reviews identify skin reactions as the most common – though typically transient – adverse effects.88, 89, 90 Device quality, electrode contact area and impedance are therefore critical factors, particularly outside controlled laboratory settings.
Fifth, brain-state dependence – fatigue, sleep loss, circadian phase, stress – can gate both the magnitude and direction of tDCS effects.91 Sleep deprivation, for example, upscales cortical excitability and alters plasticity; acute stress can potentiate stimulation effects on emotional working memory.92, 93 In sport, where load, travel and arousal vary, unmeasured state shifts could mask benefits or foster maladaptation over time.
Finally, the context of use is critical. Expert groups have cautioned against DIY enhancement, noting that protocols often drift, device quality varies and side-effect reporting is inconsistent. By contrast, remotely supervised home-use (RS-tDCS) programs employing certified hardware, impedance monitoring and telehealth oversight have demonstrated good feasibility and tolerability, suggesting a safer operational model should athletes use tDCS outside clinical settings.94, 95
Conclusions
The tDCS has moved from curiosity to a seriously discussed tool in high-performance sport. Across studies, its ergogenic effects are real but modest on average, heterogeneous across individuals and protocols, and confounded by methodological issues – features that warrant caution in interpreting headline gains. Mechanistic understanding in athletic contexts also lags behind clinical insight, and tDCS use is practically undetectable outside of self-report, which complicates governance.
Assessed against the 2021 WADA Code, the technology clearly satisfies the “potential to enhance performance” criterion and, when used explicitly for competitive advantage, raises a credible “spirit of sport” concern. By contrast, within established parameters tDCS shows a strong safety profile; the principal unknowns relate to long-term, performance-oriented use and to misuse outside supervision. Therapeutic applications under medical oversight remain ethically and regulatorily distinct.
Policy therefore sits on a knife-edge between letters and limits of the Code and what is practicable and proportionate. On the one hand, meeting 2 of 3 criteria would technically justify prohibition. On the other, enforceability is poor, the mean performance effect is small and variable, and a ban risks driving clandestine use and eroding transparency – considerations that have previously informed a “monitor rather than prohibit” stance for borderline methods.
A measured course of action follows from these findings: 1) continue open monitoring rather than immediate prohibition; 2) publish sport-specific guidance on safe, supervised use (including screening, dosing, skin care, and device quality), with clear separation between therapeutic use and performance enhancement; 3) require disclosure in elite training environments to preserve transparency; and 4) prioritize research on long-term safety, state-dependence, individual variability, and off-target cognitive trade-offs in athlete-style protocols. Should future evidence demonstrate robust, reliable and material competitive advantages – or reveal substantive health risks – revisiting inclusion on the Prohibited List would be justified. For now, the balance of scientific, ethical and practical considerations supports cautious oversight and ongoing evidence-gathering over an outright ban.
Use of AI and AI-assisted technologies
Not applicable.