Serena Williams' first tournament in her tennis comeback ended abruptly for an unexpected reason: Her doubles partner had to bow out with a knee injury. But the 44-year-old plans to play again in Germany next week, and Matthew Futterman of the Athletic sees her return to play as a test case for where sports draw the line on modern weight-loss drugs. Williams is the most high-profile athlete competing after using a GLP-1 medication, Zepbound, which she began taking post-pregnancy after struggling to lose weight through training alone. The 23-time Grand Slam champion, who serves as an ambassador for telehealth company Ro, has called the drug less a "shortcut" than a way to address biology that "wasn't working."
That framing runs straight into an unsettled debate. GLP-1 drugs like semaglutide and tirzepatide aren't banned by the World Anti-Doping Agency, but they've been under official monitoring since 2024 as potential performance aids, notes Tennis.com in its own explainer on the issue. One of the criteria WADA uses is the somewhat objective measure of whether a drug violates the "spirit of sport," writes Futterman. In the case of GLP-1s, that could come into play if athletes use them to drop weight in lieu of training.
Another factor, however, is that the drugs are still evolving. Current iterations reduce weight but can also shrink muscle and increase fatigue, complicating their impact on performance, but drugmakers are already working on versions that mitigate those side effects. That shift is seen by anti-doping officials as a "growing threat," and Williams' high-visibility use could well speed up the debate.
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