Serena Williams, WADA Monitoring, and the Questions Sports Regulators Are Starting to Ask
Last updated: June 2026 | Covers: Ozempic, Wegovy, Mounjaro, Zepbound — GLP-1 drugs in sport | Read time: ~12 min
GLP-1 receptor agonists — Ozempic, Wegovy, Mounjaro, Zepbound, and their counterparts — are usually discussed in the context of managing Type 2 diabetes, treating obesity, and reducing cardiovascular risk. As these medications have moved from specialist clinics into mainstream culture, however, a new debate has opened up in an unexpected setting: the world of competitive sport. The core question is whether medications designed to suppress appetite, alter body composition, and change metabolic function belong in a category that could be considered performance-enhancing — and whether regulators should treat them differently than they do today.
The short answer is that GLP-1 drugs are not currently banned under the WADA Prohibited List. The more complete answer is considerably more layered. Semaglutide and tirzepatide are actively being monitored by the World Anti-Doping Agency, meaning regulators are collecting data, watching usage patterns, and considering whether future rule changes are warranted. That monitoring designation — sitting somewhere between “permitted” and “under review” — reflects a genuine scientific and ethical uncertainty that the sports world has not yet resolved.
The debate became substantially more public when Serena Williams discussed her use of a GLP-1 medication following childbirth. Her case has become a reference point in the conversation, not because it suggests wrongdoing — she used a permitted medication and was transparent about it — but because it crystallizes the question: when a world-class athlete uses a drug that changes body composition and then returns to elite competition, is that simply medical weight management, or does it affect the competitive landscape in ways that regulators should be thinking about?
The Current WADA Status: Monitored, Not Banned
Under the WADA 2026 Prohibited List, which came into effect on January 1, 2026, GLP-1 receptor agonists including semaglutide and tirzepatide are not listed as prohibited substances. Athletes who use these medications for legitimate medical reasons are not in violation of anti-doping rules. USADA and other national anti-doping agencies follow the WADA framework and do not currently restrict GLP-1 drug use.
What regulators have done is place GLP-1 drugs on WADA’s monitoring program. Monitoring is a structured surveillance mechanism, not a form of restriction. Under the program, anti-doping authorities are collecting data on how frequently athletes use these medications, whether they are used in or out of competition, whether there are patterns suggesting misuse, and whether the available evidence points toward performance benefit or health risk significant enough to justify future regulatory action. It is, in essence, a watching brief.
Monitoring is not prohibition. GLP-1 drugs are currently permitted in sport. But WADA’s decision to monitor them signals that regulators believe these medications are relevant to competitive fairness or athlete health in ways that warrant ongoing scrutiny.
What WADA Considers “Performance-Enhancing”
To evaluate whether GLP-1 drugs could ever be prohibited, it helps to understand the criteria regulators actually apply. WADA can prohibit a substance if it meets at least two of the following three conditions:
- It has the potential to enhance or enhances sport performance
- It represents an actual or potential health risk to the athlete
- Its use violates the spirit of sport as defined by WADA
Classic performance-enhancing substances satisfy these conditions directly and clearly. Anabolic steroids increase muscle mass and accelerate recovery. Erythropoietin (EPO) increases red blood cell production and oxygen delivery. Stimulants sharpen alertness and aggression. All of these work through mechanisms that directly and measurably improve athletic output in ways that are not achievable through training and nutrition alone.
GLP-1 drugs operate differently. They suppress appetite, slow gastric emptying, improve insulin sensitivity, and reduce body weight. They do not directly increase muscle mass, oxygen capacity, or explosive power. Any performance relevance they have is indirect — mediated through changes in body composition and weight, which may or may not translate into competitive advantage depending on the sport, the athlete, and how the drug is managed. The question of whether that indirect pathway is sufficient to meet WADA’s criteria is the one regulators have not yet answered. It is easier to understand why when you look at what GLP-1 drugs actually do to the body — which is covered in depth in the how GLP-1 drugs work overview on this site.
How GLP-1 Drugs Could Indirectly Affect Athletic Performance
The performance question with GLP-1 drugs is genuinely two-sided. The same medication, in the same athlete, could plausibly produce both advantages and disadvantages depending on sport-specific demands, how the drug is managed, and individual physiological response. Understanding both sides is necessary for any honest evaluation.
The Case for Indirect Advantage
In sports where body weight and body composition materially affect performance, a meaningful reduction in fat mass — achieved while preserving lean mass through appropriate nutrition and resistance training — could produce real competitive benefit. The sports most commonly cited in this context include those where the athlete moves against gravity, where power-to-weight ratio is a central performance variable, or where excess weight limits agility, acceleration, or endurance capacity. In theory:
- A lighter athlete accelerates more easily and decelerates with less joint stress
- Improved power-to-weight ratio can translate directly into performance in cycling, running, climbing, and court sports
- Reduced body fat may improve metabolic efficiency and thermoregulation in endurance events
- For athletes carrying weight that was genuinely limiting their movement — as Williams described — achieving a leaner composition may restore performance capacity that had been impaired
The Case for Performance Impairment
GLP-1 drugs are not simple weight-loss tools whose effects can be cleanly separated from their other pharmacological consequences. Lean mass loss is one of the most clinically significant concerns for athletes using these medications, because clinical research consistently shows that approximately 25 to 40 percent of weight lost on GLP-1 therapy comes from lean tissue rather than fat. For an athlete whose performance depends on muscle power, rotational strength, sprint capacity, or endurance — virtually any competitive sport — losing meaningful lean mass is not a neutral outcome. It can directly impair the physical capacities that distinguish elite from non-elite performers.
The gastrointestinal effects that affect a meaningful proportion of GLP-1 users add another layer of impairment risk. Nausea, vomiting, and appetite suppression sufficient to cause inadequate energy and nutrient intake are particularly dangerous for athletes whose training demands a caloric surplus rather than a deficit. An athlete who is under-fueling because their appetite is pharmacologically suppressed is an athlete whose recovery, muscle repair, and cognitive function are all compromised. Dehydration and electrolyte depletion from persistent GI symptoms add further risk in any sport involving sustained physical effort.
| Potential Advantage | Potential Disadvantage |
| Reduced body weight in weight-sensitive sports | Lean mass loss, reducing power and strength |
| Improved power-to-weight ratio if fat mass reduced | Appetite suppression causing chronic under-fueling |
| Less joint stress and improved mobility | Nausea and GI symptoms impairing training |
| Improved metabolic efficiency in endurance sports | Dehydration and electrolyte imbalance |
| Better conditioning for athletes with obesity-related impairment | Fatigue and impaired recovery between sessions |
| Reduced excess weight improving movement economy | Reduced carbohydrate and protein availability |
The Serena Williams Question
Serena Williams became the most prominent public figure in the GLP-1 and sport debate when she discussed using a GLP-1 medication following pregnancy. Reports in 2025 stated that she lost approximately 31 pounds over several months while using the medication through a telehealth provider, and that she later returned to competitive tennis. She spoke publicly about the experience in the context of reducing stigma around weight-loss medication, framing it explicitly as a health decision rather than a performance strategy.
Her transparency matters and should be recognized. Williams did not conceal her use of a permitted medication. She was not violating any anti-doping rule. Her willingness to discuss the topic publicly has made this conversation more accessible than it would otherwise be, and the framing she provided — post-pregnancy weight management under medical supervision — is a clinically legitimate use case for GLP-1 therapy that no reasonable person would categorize as doping.
At the same time, the public response to her case illustrates exactly why sports regulators are monitoring this class of medications. Williams is not simply a celebrity who used a weight-loss drug. She is one of the most decorated athletes in the history of her sport, and her body composition, movement efficiency, and physical conditioning have always been central to her performance profile. When an athlete of that calibre uses a medication that changes body weight and composition, and then returns to elite competition, the natural questions about competitive fairness are difficult to dismiss, even if the legal answer under current rules is clear.
Williams’ case does not suggest wrongdoing. What it does is illustrate the gap between what is currently permitted and what regulators, competitors, and the public are beginning to ask. That gap is what WADA’s monitoring program is designed to help close.
GLP-1 Drugs vs. Anabolic Steroids: A Meaningful Distinction
A comparison to anabolic steroids — the archetype of prohibited performance-enhancing drugs — is worth making explicitly, because the two classes of medication work through fundamentally different mechanisms and have fundamentally different relationships to athletic performance.
Anabolic steroids directly stimulate muscle protein synthesis, accelerate recovery from training stress, and allow athletes to train harder and adapt faster than their natural physiology would permit. The performance advantage they confer is direct, substantial, and well-documented across decades of research. They work by making athletes better at the thing sport measures: physical output.
GLP-1 drugs do the opposite with respect to muscle. They do not build lean tissue. They suppress the appetite that drives nutrient intake, and in the process tend to reduce lean mass alongside fat. Their performance-relevant effects are indirect — mediated through body weight and composition changes — and those effects can just as easily impair performance as improve it, depending on how the drug is managed and what the sport demands. Describing GLP-1 drugs as the equivalent of steroids mischaracterizes both drug classes and muddies the regulatory question.
Where the Fairness Concern Is Sharpest: Weight-Class Sports
The most ethically compelling case for regulatory attention to GLP-1 drugs is not in open-weight sports like tennis, where the performance impact is ambiguous and sport-dependent. It is in competitions where body weight is itself the organizing variable of the competition. Boxing, mixed martial arts, wrestling, rowing, weightlifting, horse racing, and gymnastics are all sports in which achieving a lower weight or weight classification can directly determine who you compete against and under what conditions.
In these contexts, a medication that helps an athlete achieve and maintain a lower weight classification without the dehydration, crash-dieting, and acute nutritional deprivation traditionally associated with weight cutting raises questions that go beyond individual athlete choice. If a boxer uses a GLP-1 drug to remain comfortably in a lighter weight class while competing against opponents who achieved that weight through conventional — and more physiologically costly — means, the question of competitive fairness has genuine substance.
This is not a hypothetical that requires a famous athlete to make it concrete. The combination of widespread GLP-1 availability, aggressive telehealth marketing, and intense athletic pressure around weight creates conditions where the potential for systematic misuse in weight-class sports is real, even if it has not yet been documented at scale. The existing pressures around weight in these sports — including the documented health risks of rapid weight cutting — provide the context within which regulators are likely to become increasingly attentive to this question.
Health Risks That May Be Amplified in Athletes
Athletes face the same documented risks as all GLP-1 users, but the demands of training and competition can amplify those risks in ways that make them more clinically significant. The severe adverse reactions associated with this drug class — including gastroparesis, bowel obstruction, pancreatitis, and dehydration-related kidney injury — carry the same risk profile for athletes as for non-athletes, with the additional consideration that training places much greater demands on the physiological systems these complications affect.
The specific risks most relevant to athletes using GLP-1 drugs include:
- Lean mass loss — directly undermining the physical capacities sport demands
- Under-fueling — athletes require a caloric intake that supports both training load and recovery, and GLP-1-induced appetite suppression may prevent that
- Dehydration and electrolyte imbalance — magnified by sweat losses from training and potentially compounded by GI symptoms
- Nausea and vomiting during training or competition — a quality-of-life and performance issue with direct safety implications in some sport contexts
- Impaired recovery — inadequate protein and caloric intake between training sessions delays the muscle repair that adaptation requires
Athletes considering GLP-1 therapy should work with both a physician and a registered sports dietitian to develop a nutrition and training strategy that minimizes these risks. Protein intake, resistance training to preserve lean mass, hydration protocols, and careful management of the timing of medication relative to training and competition are all components of a responsible approach.
What Athletes Should Consider Before Using GLP-1 Drugs
For athletes who have a clinically appropriate medical reason to use a GLP-1 medication — a diagnosis of Type 2 diabetes, obesity, metabolic disease, or another qualifying condition — the medication is currently permitted under WADA rules and can be used without anti-doping consequence. The practical and medical considerations, however, go well beyond the regulatory question.
An athlete approaching this decision with appropriate care would be well-served to address the following with their medical team and, where relevant, their sport’s governing body:
- Is there a genuine medical indication for this medication, and has that been properly documented?
- What are the rules of the relevant sport’s governing body, and have those been verified through official anti-doping resources rather than assumed?
- How will lean mass loss be managed through resistance training and adequate protein intake throughout the treatment course?
- What is the nutrition strategy for maintaining appropriate caloric intake during a period of pharmacological appetite suppression, given the additional demands of training?
- How will hydration and electrolyte management be maintained, particularly in the context of GI side effects that may impair fluid intake?
- What is the timing of treatment relative to competitive season, and are there periods where the GI side effects would be most problematic?
- Does the sport require a therapeutic use exemption for this medication, or for any condition being treated alongside it?
Where the Regulatory Debate Is Heading
The trajectory of anti-doping discussion around GLP-1 drugs is not difficult to project. WADA does not place substances on its monitoring program without reason, and the reasons in this case are evident: rapidly growing use among elite and recreational athletes, high-profile public figures discussing these medications openly, documented effects on body composition that are relevant to competitive performance in weight-sensitive sports, and the absence of clear scientific consensus on whether and under what conditions a meaningful performance advantage is conferred.
Reports in 2026 have indicated that anti-doping authorities are actively considering the question of whether weight-loss medications should eventually be added to the prohibited list. That consideration is in its early stages, and the absence of strong direct evidence of performance enhancement in the competitive setting provides a reasonable basis for the current monitored-but-permitted status. But the history of anti-doping regulation shows that the window between monitoring and prohibition can close faster than athletes expect.
The safest assumption for any elite or competitive athlete is that GLP-1 drugs may not remain in their current regulatory status indefinitely, and that using a permitted medication today in a sport where body weight is competitively significant is a decision that may eventually be viewed differently by governing bodies. That does not make the decision wrong. It does make the importance of medical documentation, transparent communication with governing bodies, and careful clinical management even more significant than it might be for a non-athlete patient.
Key Takeaways
The question of whether GLP-1 drugs are performance enhancers does not have a clean answer, and anyone who offers one should be approached with skepticism. What the available evidence and regulatory landscape support is the following:
- GLP-1 drugs are not currently prohibited under WADA rules, and athletes may use them without anti-doping violation
- Semaglutide and tirzepatide are actively monitored by WADA, meaning regulators are collecting data and the status could change
- These drugs are not performance enhancers in the direct, mechanism-based sense that anabolic steroids are — they do not build muscle, increase oxygen capacity, or directly enhance sport-specific physical output
- They may indirectly affect performance through body weight and composition changes, with effects that can be advantageous or harmful depending on the sport, the athlete, and how the medication is managed
- The risks of lean mass loss, under-fueling, dehydration, and GI symptoms may be amplified in athletes whose training demands exceed what a pharmacologically suppressed appetite can support
- Weight-class sports raise the sharpest fairness questions and are likely to draw the most regulatory scrutiny over time
- Serena Williams’ reported use of a GLP-1 medication has become a major public reference point in this debate, but it represents a permitted, transparent use of medication for a legitimate medical purpose — not a doping violation
- The ethical, medical, and regulatory dimensions of GLP-1 use in sport remain unsettled and will continue to evolve as prescribing grows, evidence accumulates, and regulators respond