Serena Williams's GLP-1 Use Puts Sports Regulators in an Uncomfortable Spot

Since our earlier coverage this week of GLP-1 drugs and athletic performance, a concrete test case has materialized on a professional court.

Serena Williams, 44, competed in doubles at the Queen's Club tournament in London alongside 19-year-old Victoria Mboko. The pair beat the third seed in their opening match. Williams closed it out with a 116-mile-an-hour serve. She is scheduled to play doubles again with her sister Venus at Wimbledon.

Williams is a paid spokesperson for Ro, a telehealth company specializing in GLP-1 prescriptions. She has said publicly that she lost 34 pounds using tirzepatide and that the drug helped manage her cholesterol. Importantly, she told People magazine in August that the medication "helped me enhance everything that I was already doing — eating healthy and working out, whether it was as a professional athlete at the top level of tennis or just going to the gym every day."

That quote is the reason regulators are paying attention.

What WADA Actually Says

The World Anti-Doping Agency has NOT banned GLP-1 drugs. Athletes can take them today with no penalty. WADA told The Atlantic it is monitoring whether they are being abused, but has issued no formal review timeline.

The agency's own experts are split. Thomas Hudzik, a pharmaceutical consultant who has served on the advisory group that recommends what WADA should ban, told The Atlantic he sees little competitive advantage: "I can't see that there would be much of an advantage at all to using these substances in an athlete."

Lars Engebretsen, head of WADA's health, medical, and research committee, told the Norwegian Broadcasting Corporation a different thing: the drugs probably should be banned, though his stated reason is concern about eating disorders in athletes, not direct performance enhancement.

Two senior voices at the same agency, two opposite conclusions.

The Honest Case for Concern

Skeptics of a ban deserve a fair hearing. Their concern is not paranoid. GLP-1 drugs reduce body fat, potentially improving power-to-weight ratios in weight-class sports, endurance events, and anything requiring explosive movement. They also appear to reduce inflammation, according to emerging research cited in the sources. However, being lighter is not straightforwardly an advantage: roughly 25 to 35 percent of the weight that GLP-1 patients lose is lean mass, according to a meta-analysis published in March. Athletes using GLP-1s will need to closely manage diet and training to maintain muscle. The comparison to substances that improve physical performance in ways that also have legitimate medical uses is not crazy.

A Ro spokesperson responded that "any patient who receives a GLP-1 prescription through Ro has been determined to be clinically eligible for that treatment by a licensed medical provider." That is true of many substances WADA bans. Clinical eligibility and competitive fairness are separate questions.

The Problem: No Data

Regulators face a central obstacle: no controlled studies have tested GLP-1 drugs specifically in elite athletes. Every expert opinion in this debate, including Engebretsen's call for a ban, is extrapolated from general-population studies. Williams's comeback, as The Atlantic noted, is one of the first observable data points available. It is a single anecdote about a 44-year-old returning from a nearly four-year absence, not a randomized trial. Her results have also been uneven: she won with Mboko at the Queen's Club but lost her first doubles match at the Berlin Open.

Williams's publicist declined to confirm to The Atlantic whether she is still taking tirzepatide. So the scientific value of watching her perform is limited: we do not know her current drug status, her dosage history, or what her baseline fitness would have looked like without it.

What Comes Next

WADA's standard process for adding a substance to its prohibited list requires that it meet two of three criteria: it enhances performance, it poses a health risk, or it violates the spirit of sport. Engebretsen has staked a position on the health-risk angle. Hudzik's position implies the performance-enhancement angle is weak. The third criterion — spirit of sport — is the most subjective and hardest to litigate.

The practical difficulty is that GLP-1s have legitimate, documented medical uses for obesity and type 2 diabetes. Banning them outright would force athletes with genuine metabolic conditions to choose between their health and their careers, the same tension that exists with therapeutic use exemptions for other medications.

WADA is funding a trial to test how semaglutide changes runners' body composition and performance, but results are not yet available. Williams's Wimbledon doubles appearance will draw more attention to this question, but it will not answer it. As of now, WADA has not announced a formal review, no study of GLP-1 effects in elite athletes has been published, and the agency's own senior officials cannot agree on what the drug does to competitive performance. Until there is data, any ban or clearance is based on inference.