Anti-doping agencies monitor GLP‑1 weight‑loss injections after traces found in sport; experts warn of performance and health risks

The World Anti‑Doping Agency and national anti‑doping authorities are monitoring popular prescription weight‑loss injections such as semaglutide and tirzepatide after metabolites were detected in out‑of‑competition drug tests, prompting fresh scrutiny over their use in sport.

A confidential WADA document circulated to stakeholders in July shows semaglutide was screened for in 8,402 out‑of‑competition urine samples, with two positive findings for metabolites common to semaglutide and tirzepatide. One of the positives came from cycling and the other from rugby league. WADA and the U.S. Anti‑Doping Agency (USADA) say the number is tiny but enough to justify closer observation as both substances are placed on monitoring lists rather than being prohibited at present.

WADA’s monitoring programme is designed to gather intelligence on emerging substances so the organisation can determine whether they meet the criteria for a ban: potential to enhance performance, a demonstrated health risk to athletes, and violation of the spirit of sport. "We are not there yet," said Professor Olivier Rabin, WADA’s head of science, adding that WADA expects studies into semaglutide and tirzepatide to continue into 2026. Rabin confirmed the July document and said the agency would look for patterns such as multiple finds linked to the same team or sport before moving toward prohibition.

USADA officials have expressed similar caution. Dr. Matthew Fedoruk, USADA’s chief science officer, said blockbuster sales and widespread recreational use make these drugs of interest to anti‑doping authorities. "When you're looking at emerging drugs like this that have become blockbuster drugs, then there is obviously a concern," he said. "The jury is still out on whether we fully understand its use. We're hearing at the recreational level, but not at the elite. That being said, trends that start at the recreational level have a tendency to be abused at the elite level as well."

The GLP‑1 receptor agonists that include semaglutide (marketed as Ozempic and Wegovy) and tirzepatide (Mounjaro and Zepbound) have attracted millions of users worldwide after clinical trials showed strong weight‑loss effects. More than 500,000 people in the U.K. are estimated to be taking weekly injections, and U.S. surveys have suggested around one in eight adults have tried the drugs. High‑profile public figures, including retired athletes and entertainers, have spoken publicly about using the injections.

Anti‑doping and sports scientists caution that the physiological effects that make GLP‑1 agonists effective for weight loss are likely to be counterproductive for many elite athletes. Studies have linked semaglutide to a loss of lean muscle mass of up to about 10 percent. Side effects can include nausea, vomiting, dizziness, blurred vision and diarrhoea—symptoms that can impair training and competition.

"Based on the muscle loss that we have seen reported, it’s the antithesis of what you are trying to achieve," said Greg Whyte, professor of applied sport and exercise at Liverpool John Moores University and a former Team GB Olympian. He added that appetite suppression can reduce fuel for training, lower session quality and slow recovery, which would undermine athletic performance.

Experts said the balance of risk and benefit will vary by sport. Combat sports and other disciplines that require extremely high caloric expenditure during training are unlikely to favour chronic appetite suppression. Speedy, last‑minute weight cuts—such as those undertaken in boxing before a weigh‑in—are also a poor match for injections that operate over weeks or months. But horse racing may be an exception, sources said. Jockeys frequently maintain weights that are well below their natural set point and may face relentless pressure to keep hunger suppressed; their daily caloric expenditure is often lower than that of combat athletes, and some within the industry say the drugs’ appeal warrants vigilance.

Paul Struthers, chief executive of the Professional Jockeys Association, said racing officials are "acutely alive" to the issue and are educating riders about risks. He and other racing figures said they had not heard of widespread use among professional jockeys, while acknowledging the small size of the workforce and the constant pressure to manage weight could make isolated experimentation plausible.

Anti‑doping officials also warn about the potential for future combinations of drugs to blunt known disadvantages. Dr. Fedoruk pointed to clinical research exploring combinations that might mitigate muscle loss, such as pairing semaglutide with androgen receptor modulators. "One of the things that we're particularly interested in is these clinical trials that are happening where you've got synergistic effects… and you actually prevent that muscle loss by up to 70 per cent," he said. Such combinations, if they were developed and then diverted into sport, could alter the risk calculus for athletes and complicate detection strategies.

At present, WADA’s monitoring remains focused on understanding prevalence, patterns of use and the potential for performance effects or health harms. Detecting metabolites in urine confirms exposure in isolated instances, but WADA officials say a move to prohibition would hinge on more robust evidence that the substances are being used deliberately to gain an unfair advantage or pose substantial health risks to athletes.

Professionals who work closely with athletes emphasised that the medications are prescription‑only therapies developed for people with obesity or certain metabolic conditions and that misuse carries medical and ethical concerns. "To anyone informed in elite sport, it would be a no‑brainer not to take it," Whyte said, noting the contrast between perceived quick fixes and the nutritional demands of elite performance.

Athletes have already appeared publicly with the injections. Retired tennis champion Serena Williams featured in promotional material for a telehealth service while photographed administering an injection. Former athletes and celebrities have publicly noted use, and anecdotal reporting has included a small number of former professional competitors taking the drugs in retirement. Apart from those anecdotal accounts and the two positive tests, however, authorities say there is not yet evidence of organized or widespread elite‑level use.

Anti‑doping agencies say they will continue surveillance, testing and research to determine whether the monitoring classification should escalate. In the meantime, scientists and governing bodies are urging athletes to weigh the documented risks against unclear performance benefits and to consult medical professionals before considering prescription weight‑loss treatments.

"There is a potential for abuse," Rabin said, "but right now we need more data and clear patterns to make a regulatory decision."