Anti-doping agencies monitor rise of weight‑loss injections as tests detect traces in sport

World Anti‑Doping Agency and national anti‑doping bodies have placed recently popular weight‑loss injections built on GLP‑1 drugs under close scrutiny after metabolites linked to those medicines were detected in out‑of‑competition tests, though the substances remain legal for now in elite sport.

A confidential WADA report circulated to stakeholders showed semaglutide metabolites were monitored in 8,402 urine samples, with two positive findings reported last year — one from cycling and one from rugby league. WADA and the U.S. Anti‑Doping Agency (USADA) say the detections amount to a trickle rather than an established pattern, and that further study is underway before any decision to move the drugs from a monitoring list to a prohibited list.

WADA’s head of science, Professor Olivier Rabin, told media outlets the agency has placed semaglutide on its monitoring list while extending studies into 2026 and has also begun watching tirzepatide. The two compounds, sold under brand names such as Ozempic, Wegovy, Mounjaro and Zepbound, act on glucagon‑like peptide‑1 pathways to suppress appetite and slow digestion. Dr. Matthew Fedoruk, USADA’s chief science officer, said both agencies are examining whether the drugs could be abused in sport and are monitoring clinical trials that combine GLP‑1 therapies with other agents that might blunt muscle loss.

Anti‑doping authorities apply scientific and ethical tests before moving a substance to the prohibited list. Under WADA’s criteria, a drug must meet at least two of three conditions — potential performance enhancement, health risk to athletes, or violation of the spirit of sport — to justify prohibition. Officials say the current evidence does not yet meet those thresholds, but they are watching for patterns such as multiple positives from a single team or sport.

The drugs’ rapid adoption in the general population has heightened those concerns. High‑profile public figures and former athletes have publicly credited GLP‑1 injections for weight loss, and promotional images have surfaced showing retired tennis champion Serena Williams posing with an injector as part of a telehealth advertisement. Anti‑doping officials stressed there is no public, verified evidence that leading active competitors are using the drugs, and much of the uptake to date has been at the recreational level among amateur runners, triathletes and cyclists.

Experts consulted by news outlets and anti‑doping officials note several medical and performance factors that could deter elite athletes. Clinical studies and reports indicate semaglutide can reduce lean muscle mass by as much as about 10 percent. Side effects documented in clinical use include nausea, vomiting, dizziness, blurred vision and diarrhea — effects that medical and sports scientists warn would impair training and competition.

"We are not there yet," Professor Rabin said of banning the drugs. "Of course, some athletes would be tempted. This is why we are concerned about risk of abuse." Professor Greg Whyte, an applied sport and exercise scientist, said the medications run counter to the needs of most elite athletes because appetite suppression reduces fuel for high‑quality training and slows recovery. "Everything about GLP‑1 points in the opposite direction to what you're trying to achieve as an elite athlete," he said.

Those performance drawbacks have framed discussion about which sports, if any, might be more susceptible to use. Anti‑doping and sports medicine sources view combat sports, cycling and gymnastics as unlikely candidates because athletes require large caloric intakes for training or rapid weight changes before competition, and the medications act too slowly to be useful for last‑minute weight cutting. Horse racing is considered a potential outlier because professional jockeys maintain unnaturally low body weights for extended periods, often with lower day‑to‑day caloric expenditure than other athletes.

Paul Struthers, chief executive of the Professional Jockeys Association, said the industry is "acutely alive" to the possibility that riders might be tempted to seek shortcuts and that education efforts are under way. Jockeys and trainers interviewed for this article said they had not heard of widespread use but acknowledged the pressure of chronic weight management creates vulnerability to new interventions. Retired jockey Adam Kirby said such injections "would make no sense" for riders because they need to be fully alert and maintain leg strength and cardiovascular fitness.

Some anti‑doping scientists have flagged a more complex risk: the potential combination of GLP‑1 therapies with other substances intended to preserve or build muscle. Dr. Fedoruk pointed to clinical research testing synergistic effects of semaglutide alongside agents such as selective androgen receptor modulators (SARMs), which are prohibited in sport. Those combinations, if adopted illicitly, could blunt the drugs’ muscle‑loss side effects and increase temptation for athletes seeking a weight‑management advantage.

Evidence so far is limited. WADA confirmed the two positive semaglutide‑linked findings from its monitoring exercise but emphasized the sample size needed to establish a pattern would be much larger. USADA officials described reports of recreational use but said they have not seen clear evidence of the drugs at the elite level. Anti‑doping agencies say they will continue to analyse samples, monitor clinical literature and develop testing capabilities so that any change in prevalence or misuse can be assessed promptly.

Medical specialists caution athletes against unsupervised use of GLP‑1 therapies. The drugs are prescription medicines intended to treat obesity and metabolic conditions, and prescribing guidance typically pairs them with lifestyle and clinical monitoring. Sports scientists have stressed that the medications are not a straightforward performance aid and could harm athletes’ strength, endurance and recovery.

For now, WADA’s monitoring, the limited number of positive detections and cautionary statements from scientific staff leave the drugs in a watch‑and‑wait position. Anti‑doping bodies say the trajectory could change if further testing turns up a heavier signal in specific sports or teams, or if clinical trials demonstrate combinations that would materially alter the drugs’ effects on lean mass. Until then, officials and sports medicine experts emphasise education, surveillance and research as the primary responses to a fast‑growing class of medications that has already reshaped conversations about weight management outside sport.