When Serena Williams told reporters that starting a GLP 1 medication sooner might have changed the outcome of some matches in her career, she was not talking about diabetes management. She was talking about winning. That comment, made almost in passing, is the reason a class of drugs built for blood sugar control and obesity treatment is now sitting inside a conversation usually reserved for anabolic steroids and blood doping.
The World Anti Doping Agency has not banned semaglutide, the active ingredient in Ozempic and Wegovy, or tirzepatide, the ingredient in Mounjaro and Zepbound. Both remain legal for athletes to use, in competition and out of it, without a medical exemption. But WADA has placed markers of both drugs on its Monitoring Program, the formal watchlist it uses to track substances that are not yet prohibited but might eventually meet the bar for a ban. That distinction, between watched and banned, is easy to miss and important to understand, because it explains why this story is not really about a rule that already exists. It is about the evidence that is currently being gathered to decide whether a new one should.
To understand why regulators are paying attention at all, it helps to know what these drugs actually do inside the body, why athletes in weight sensitive sports would be tempted to use them, and why the same biology that makes them effective for weight loss might make them a liability in competition rather than an advantage.
From a Lizard’s Venom to a Pharmaceutical Phenomenon
The active ingredients behind Ozempic, Wegovy, Mounjaro and Zepbound trace back to an unlikely source. Exenatide, the first drug in this class, was derived from exendin 4, a compound found in the saliva of the Gila monster, a lizard native to the southwestern United States that can survive long stretches without eating. Researchers noticed that the compound mimicked a human hormone called glucagon like peptide 1, or GLP 1, which the gut releases after eating to help regulate blood sugar. The FDA approved exenatide in 2005 as a treatment for type 2 diabetes, and the drug class has expanded rapidly since then.
GLP 1 acts on the pancreas to increase insulin release, slows down how quickly the stomach empties food into the intestine, and sends signals to the brain that reduce appetite. Semaglutide and tirzepatide are synthetic versions of this signalling pathway, engineered to last far longer in the bloodstream than the natural hormone, which is broken down within minutes. Tirzepatide goes a step further by also activating a second hormone receptor, GIP, which appears to amplify both the blood sugar and appetite effects.
What began as a diabetes treatment became something else entirely once clinical trials showed the weight loss effects were large and durable. In Novo Nordisk’s STEP 1 trial, participants taking semaglutide lost an average of 15 percent of their body weight over 68 weeks. Eli Lilly’s SURMOUNT 1 trial found tirzepatide produced weight loss between 15 and 21 percent over 72 weeks. Those numbers, published in peer reviewed journals, are what turned a niche diabetes therapy into one of the most commercially significant drug categories in modern medicine. Industry estimates place the global GLP 1 drug market at roughly 53 to 58 billion dollars in 2026, with projections from firms including J.P. Morgan Global Research suggesting the broader incretin market could reach 200 billion dollars by 2030 as oral formulations and expanded insurance coverage widen access.
Why a Diabetes Drug Caught the Attention of Sports Regulators
The logic pulling GLP 1 drugs into an anti doping conversation is straightforward once you consider which sports reward a lower body weight. In cycling, distance running, triathlon, gymnastics, and any weight class sport from boxing to wrestling, an athlete’s power to weight ratio or ability to make a specific weight bracket can matter as much as raw strength or aerobic capacity. A drug that reliably strips body weight without requiring the punishing caloric restriction athletes have traditionally relied on is, at least in theory, an attractive shortcut.
That theoretical appeal is exactly what pushed WADA to add semaglutide and tirzepatide markers to its Monitoring Program. According to the Athletics Integrity Unit’s official summary of the 2026 WADA Prohibited List, the agency monitors substances under Article 4.5 of the World Anti Doping Code specifically to detect patterns of misuse before deciding whether a formal ban is warranted. For 2026, markers of semaglutide and tirzepatide are tracked both in competition and out of competition, alongside substances such as ecdysterone and hypoxen. Crucially, the Monitoring Program carries no sanctions. An athlete found to have used a monitored substance faces no anti doping violation. The data collected simply feeds into WADA’s future decisions about whether the drug meets the criteria for prohibition.
Those criteria, laid out under the World Anti Doping Code, require that a substance meet at least two of three conditions before it can be added to the banned list: it enhances or has the potential to enhance performance, it poses a health risk to the athlete, or its use violates the spirit of sport. GLP 1 drugs sit in an unusual position relative to those three tests, because the clinical evidence on whether they genuinely improve athletic performance is thin, and much of what exists points in the opposite direction.
The Muscle Loss Problem That Complicates the Doping Case
This is the part of the story that rarely makes it into headlines built around a Wimbledon champion’s TV commercial. Losing weight on a GLP 1 drug does not mean losing only fat. Multiple clinical studies have found that a meaningful share of the weight lost comes from lean tissue, including skeletal muscle, the tissue athletes depend on for power, speed and recovery.
The body composition substudy from Novo Nordisk’s STEP 1 trial found that roughly 38 to 39 percent of total weight lost on semaglutide came from lean tissue, a figure that was widely discussed among clinicians when the results were published. A subsequent reanalysis adjusted that figure downward by accounting for the fat free mass that is unavoidably lost alongside adipose tissue, bringing the semaglutide figure closer to 30 percent. A separate systematic review of six clinical trials covering 1,541 adults found that lean mass reductions ranged from close to zero up to 40 percent of total weight lost, depending on the study and the population. The SURMOUNT 1 substudy for tirzepatide reported a somewhat lower figure, around 25 percent. Regardless of the exact percentage, the consistent finding across this research is that a real portion of the weight these drugs remove is muscle, not just fat.
For a recreational user managing obesity, some lean mass loss is an accepted tradeoff against the substantial health benefits of a 15 to 20 percent reduction in body weight, including improved cardiovascular risk markers. For a competitive athlete, muscle is the raw material of performance. Reduced skeletal muscle mass can translate directly into lower power output, slower sprint speed, and diminished capacity to recover between training sessions or competitive rounds. Experts interviewed by Yahoo Sports on the question of an Olympic ban noted that GLP 1s could theoretically benefit athletes in sports where power to weight ratio or weight class requirements matter, but that the same mechanism driving weight loss, appetite suppression, creates a genuine risk of underfueling that can just as easily undermine performance as improve it.
There is a second physiological complication specific to competition. GLP 1 drugs slow gastric emptying, meaning food sits in the stomach longer before moving into the digestive tract. That effect is central to how the drugs suppress appetite, but it is a serious liability for an endurance athlete who needs to eat and hydrate strategically before and during a race. A pre race meal that would normally digest in time for a marathon start could instead sit undigested, increasing the risk of nausea, cramping or vomiting during exertion. Reporting from sports nutrition specialists at a review focused on endurance athletes describes this fueling conflict as one of the most practical reasons GLP 1 use and competitive training do not mix well, independent of any anti doping consideration.
What the Case Against Calling GLP 1s Performance Enhancing Actually Rests On
Sports medicine physicians who have weighed in publicly on this question tend to land in similar territory, even when they frame it differently. One perspective, described by a sports medicine physician in coverage from Healthline’s reporting on the debate, is that GLP 1 drugs can produce indirect improvements in energy, mood and endurance for some users, alongside the more established benefits to insulin resistance and body fat composition. That same reporting also cites the founder of a telehealth prescribing platform arguing that the strongest case against classifying GLP 1s as performance enhancing drugs is that, on balance, they are more likely to hurt athletic performance than help it, because of the muscle loss and underfueling risks already described.
A separate physician quoted in coverage of Williams’s endorsement deal framed the issue as a tradeoff rather than an advantage. Athletes who choose to use a GLP 1 drug are, in this view, choosing improved metabolic health at the cost of some muscle mass and a period of reduced athletic capacity while their body adjusts. That framing treats the drug as a health decision an athlete makes despite a performance cost, not because of a performance benefit, which is a meaningfully different category than the one occupied by anabolic steroids or erythropoietin, drugs that are used specifically because they make athletes measurably faster or stronger with no meaningful health tradeoff for the healthy user.
This is also why WADA’s own three part test is difficult to satisfy cleanly here. The health risk criterion is easier to argue, given the established muscle loss data and the risk of low energy availability the drugs can create in athletes who are already training at high volumes. But the performance enhancement criterion, the one that has driven bans on substances from testosterone to EPO, does not yet have strong supporting evidence for GLP 1 drugs specifically. A review focused on endurance athletes concluded plainly that current evidence does not show an inherent performance enhancing effect of GLP 1 agonists in healthy athletes, and that side effects on fueling and muscle mass could impair rather than improve performance.
What History Teaches About Substances Stuck in Regulatory Limbo
GLP 1 drugs are not the first substances to sit in this uncomfortable middle zone between clearly permitted and clearly banned, and looking at how similar cases resolved offers a useful sense of what might come next. Caffeine is perhaps the most instructive example. WADA removed caffeine from its Prohibited List in 2004 after concluding that its widespread, legitimate use in everyday life made a ban impractical to enforce, even though research had shown it could modestly improve endurance performance. Caffeine has remained on the Monitoring Program ever since, watched but never restored to prohibited status, because the evidence never tipped clearly enough toward the kind of unfair advantage that justifies a ban on a substance found in coffee and energy drinks consumed by a large share of the general population.
Beta blockers took a different path. These heart medications, prescribed for conditions including high blood pressure and anxiety, reduce hand tremor and heart rate in ways that offer a clear and measurable advantage in precision sports such as archery and shooting. Because the performance benefit in those specific disciplines is well documented and significant, beta blockers remain prohibited, but only in the particular sports where the steadying effect matters, while athletes in other disciplines can use them for legitimate medical reasons without restriction. That sport specific approach shows that WADA does not have to choose between a blanket ban and no restriction at all. It can, and has, tailored prohibition to the disciplines where a substance actually confers an edge.
Ecdysterone, a plant derived compound sold in some bodybuilding supplements, offers perhaps the closest parallel to where GLP 1 drugs sit today. It has been on WADA’s Monitoring Program for several years, based on early research suggesting possible anabolic effects on muscle tissue, but has not been added to the Prohibited List because the evidence for a genuine performance benefit in humans has remained inconclusive despite ongoing scrutiny. Ecdysterone’s extended stay on the watchlist illustrates that being monitored is not a holding pattern with a predetermined endpoint. Some substances spend years there before regulators either find sufficient evidence to justify a ban or conclude the case never solidifies enough to warrant one.
These precedents matter for how athletes, coaches and sports organizations should read the current GLP 1 situation. A substance landing on the Monitoring Program is not a signal that prohibition is inevitable, and it is not a loophole that will certainly stay open either. It is a genuinely open question, and the resolution depends on data that does not yet exist in sufficient volume, specifically evidence of whether athletes are using these drugs in ways that meaningfully change competitive outcomes, and whether that use is happening at a scale that concerns regulators enough to act.
Where Individual Sports Federations Stand Right Now
Because WADA’s Monitoring Program carries no sanctions, the practical rules an athlete faces depend heavily on which sport and which country they compete under. World Athletics, the global governing body for track and field, follows the WADA Code directly through the Athletics Integrity Unit, meaning GLP 1 drugs remain permitted for its athletes in 2026, subject to ongoing monitoring. Other endurance sport federations have generally aligned with the same WADA framework rather than introducing sport specific restrictions ahead of a global decision.
This creates an unusual situation compared with most doping controversies, where the rules are already settled and the debate is about enforcement or detection. Here, the rules themselves are still being written, and the data WADA collects over the next several years, drawn from testing patterns, prevalence studies and any evidence of misuse that surfaces, will shape whether GLP 1 drugs eventually join the Prohibited List or are quietly removed from monitoring once the agency concludes they do not meet the threshold for a ban. Substances have historically spent between two and five years on the Monitoring Program before a final decision is made, based on patterns WADA has followed with other watched substances.
Therapeutic Use and the Athletes Who Need These Drugs for Medical Reasons
None of this uncertainty affects the athletes who use GLP 1 drugs for their intended medical purpose. An athlete diagnosed with type 2 diabetes who is prescribed semaglutide by a physician is using the drug exactly as regulators anticipated when they approved it, and that use is currently permitted without any special exemption, since the drug is not on the Prohibited List. If WADA does eventually move GLP 1 drugs to prohibited status, athletes with a genuine, documented medical need would still be able to apply for a Therapeutic Use Exemption, the same mechanism that allows athletes with asthma to use certain inhalers or athletes with ADHD to use stimulant medication under medical supervision.
That distinction matters because it separates the medical use case from the more contested one: athletes without diabetes or a qualifying obesity diagnosis using these drugs specifically to manage competition weight or improve body composition for aesthetic or performance reasons. The United States Anti Doping Agency has warned athletes that being properly diagnosed and prescribed an FDA approved version of a GLP 1 drug matters for reasons well beyond sport rules. USADA specifically flags the growing market for unapproved, compounded, or counterfeit versions of these drugs sold online without a prescription, noting that products claiming to be generic Ozempic, Wegovy or Zepbound should be treated as a red flag, since no legal generic versions currently exist. Athletes sourcing medication outside a legitimate prescribing relationship face both a health risk from unregulated product quality and a greater likelihood of using something that could trigger an anti doping violation if it contains an undisclosed prohibited substance.
What This Means for How Athletes and Coaches Should Think About These Drugs
For an athlete considering a GLP 1 medication, medically indicated or otherwise, the practical evidence points toward a few clear considerations that have nothing to do with anti doping status. Clinical research on muscle preservation during GLP 1 treatment consistently shows that resistance training and higher protein intake meaningfully offset lean mass loss. A case series published in a peer reviewed physiology journal followed three patients who combined semaglutide or tirzepatide with structured resistance training four to seven days a week and protein intake as high as 2.3 grams per kilogram of fat free mass, and found some participants preserved or even slightly increased lean soft tissue despite substantial total weight loss. Separately, the SEMALEAN study, following 106 adults with obesity on semaglutide for a year, found that while lean mass declined by around 3 to 5 percent in the first seven months, it then stabilized, and handgrip strength actually improved by an average of 4.5 kilograms over 12 months, alongside a drop in the prevalence of sarcopenic obesity from 49 percent to 33 percent among participants. Notably, that improvement occurred without any structured exercise program being prescribed to participants.
That research suggests the muscle loss risk is real but not fixed. Athletes and their medical teams who treat a GLP 1 prescription as a metabolic health decision requiring the same disciplined attention to training load, protein intake and fueling strategy that any major change in body composition demands appear far more likely to preserve the physical qualities their sport depends on. Athletes who instead treat the drug as a passive shortcut to a lower number on the scale are the ones most likely to experience the underfueling, gastrointestinal disruption and strength loss that sports physicians consistently flag as risks.
The Regulatory Question Sport Has Not Answered Yet
The deeper tension in this story is not really about semaglutide or tirzepatide specifically. It is about how anti doping regulation is built to respond to drugs designed for one purpose that unexpectedly intersect with elite sport. Historically, substances that reach WADA’s radar tend to have a clearer performance rationale from the outset, whether that is oxygen carrying capacity, muscle protein synthesis, or central nervous system stimulation. GLP 1 drugs are different because their primary and best documented effect, appetite suppression and metabolic improvement, produces weight loss as a side effect rather than a targeted athletic adaptation, and that weight loss comes bundled with a muscle loss cost that works against many of the outcomes a ban would normally exist to prevent.
Whether that distinction is enough to keep GLP 1 drugs off the Prohibited List permanently, or whether newer formulations designed specifically to reduce muscle loss, several of which are already in clinical trials from companies including Regeneron, eventually tip the balance toward genuine performance enhancement, is a question WADA’s Monitoring Program exists precisely to answer. For now, the honest answer to whether a drug built for diabetes and obesity should be treated as a performance enhancing substance is that the evidence does not support it, but the agencies responsible for the integrity of sport are watching closely enough to change that conclusion if the data eventually says otherwise.
Common Questions About GLP 1 Drugs and Sport
Are Ozempic and Wegovy currently banned by the World Anti Doping Agency?
No. As of the 2026 WADA Prohibited List, semaglutide and tirzepatide are not banned substances. They sit on WADA’s Monitoring Program, which tracks potential misuse without imposing any sanctions on athletes who use them.
What is the difference between WADA’s Monitoring Program and the Prohibited List?
The Prohibited List contains substances and methods that trigger an anti doping violation if detected. The Monitoring Program tracks substances that are not banned but that WADA wants more data on before deciding whether they should be added to the Prohibited List in the future.
Do GLP 1 drugs actually improve athletic performance?
Current clinical evidence does not show a clear performance enhancing effect in healthy athletes. Some research points to potential downsides, including muscle loss and appetite suppression that can make it difficult to fuel properly for training and competition.
How much muscle do people typically lose on semaglutide or tirzepatide?
Clinical trial data varies, but several studies estimate that roughly 25 to 40 percent of total weight lost on these drugs comes from lean tissue rather than fat, though structured resistance training and higher protein intake appear to reduce that share significantly.
Can an athlete get in trouble for using a GLP 1 drug right now?
No, provided the drug is not itself contaminated with a prohibited substance. Since GLP 1 drugs are not on the Prohibited List, using one currently does not constitute an anti doping rule violation under the WADA Code.
Would an athlete need a medical exemption to use a GLP 1 drug if it becomes banned?
If WADA moves GLP 1 drugs to the Prohibited List in the future, athletes with a genuine medical need, such as a type 2 diabetes diagnosis, would likely be able to apply for a Therapeutic Use Exemption, the same process used for other legitimately prescribed medications.
Why did Serena Williams’s comments draw attention to this issue?
Williams, a professional tennis champion, became a paid spokesperson for a telehealth company promoting GLP 1 medications and suggested publicly that starting the drugs sooner might have affected the outcome of some matches in her career, which raised questions about where medical use ends and competitive advantage begins.
Do GLP 1 drugs slow down digestion in a way that affects competition?
Yes. These drugs delay gastric emptying as part of how they suppress appetite, which can interfere with pre competition fueling strategies and increase the risk of gastrointestinal discomfort during exertion.
Is it risky to buy GLP 1 drugs online without a prescription?
Yes. Anti doping and health authorities warn that unapproved or compounded versions sold without a legitimate prescription carry both health risks from unregulated manufacturing and a higher chance of containing undisclosed substances.
How long do substances typically stay on WADA’s Monitoring Program before a final decision is made?
There is no fixed timeline, but historically substances have remained on the Monitoring Program anywhere from two to several years while WADA gathers enough data to determine whether prohibition is justified.
