News and Analysis

Before Serena Williams picked up her racket at London’s Andy Murray Arena last week, two questions hung over her return to tennis.First: How would she do? She answered that, in her first competition in nearly four years, by winning. The 44-year-old and her doubles partner, the 19-year-old Victoria Mboko, ended up besting the third seed in their opening match of the Queen’s Club tournament. Their victory was sealed by a 116-mile-an-hour serve from Williams that her opponents couldn’t return.The second will take longer to answer: Did a GLP-1 weight-loss drug enhance her performance?Williams is a paid spokesperson for Ro, a telehealth company that specializes in such medications. In ads, she says that she lost 34 pounds with the help of GLP-1s. It’s unclear whether Williams is still on her drug of choice, tirzepatide (her publicist declined to comment), which has helped her lose stubborn baby weight and manage her cholesterol. Although there’s no indication that she took it to gain a competitive advantage, Williams has also said that the medication improved her training and her game. The drug “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,” she told People magazine in August.With her comeback, Williams is the first active elite athlete to publicize her use of GLP-1s. But the world of sports is full of whispers that she is not the only one. The more athletes who follow Williams’s lead, the more urgent the question of whether GLP-1s should be treated as performance-enhancing drugs will become.The World Anti-Doping Agency, which sets rules adopted by most international sporting leagues, has said that it is keeping a close eye on whether GLP-1s are being abused; for now, athletes are free to take them. (A Ro spokesperson told me 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.”) But experts are divided over whether GLP-1s have the potential to improve athleticism. “I can’t see that there would be much of an advantage at all to using these substances in an athlete,” Thomas Hudzik, a pharmaceutical consultant who has served on the advisory group that recommends what drugs WADA should ban, told me. Meanwhile, Lars Engebretsen, the head of WADA’s health, medical, and research committee, told the Norwegian Broadcasting Corporation that he believes the drugs should be banned, but mostly because they could exacerbate eating disorders.Opinions diverge because no studies have yet tested these drugs in elite athletes. Williams’s return to tennis—which will continue with a doubles appearance alongside her sister Venus at Wimbledon—is one of the first opportunities, as far as we know, to see how an elite athlete performs after taking a GLP-1. So far, the results have been uneven: She won with Mboko at the Queen’s Club, but lost her first doubles match at the Berlin Open this week. Doubles also demands less of athletes than a singles match does, so Williams’s full abilities have not yet been tested in competition. (Tennis fans are eager to know if Williams will get a wild-card singles spot at Wimbledon too.) “The jury is out in terms of endurance, stamina,” Rick Macci, who trained Williams during her childhood, told me.[Read: America has a new GLP-1 playbook]Being trim can be an advantage in some sports. A lighter frame can reduce the amount of effort needed for, say, climbing, running, or gymnastics. And weight is built into the structure of other sports. Wrestlers, for example, must weigh in to qualify for their matches. The popular strategy is to get just under the maximum weight for a given class—a process that GLP-1s might make easier. “It makes perfect sense in weight-category sports,” John Hawley, the director of Australian Catholic University’s Centre for Human Metabolism and Performance, told me via email.But whether GLP-1s will deliver meaningful weight loss for athletes already in tip-top shape is an open question. No major trials have tested GLP-1s in healthy people with a normal or low BMI, so it’s unclear how much weight such people might lose on the drug. That could mean that among elite athletes, the drugs might have significant effects for only a small group, including Williams, who are seeking to get back into shape. Several clinical trials have also shown that GLP-1s can reduce an inflammation marker in the blood—but it’s still unclear how much of that improvement is the result of weight loss or an independent effect of the drugs.Besides, being light isn’t necessarily an upside if it means a reduction in strength. 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 watch their diet and training to make sure they maintain muscle (perhaps while dealing with the vomiting, nausea, and diarrhea often associated with GLP-1s). Plus, GLP-1s are believed to dampen dopamine signaling, which “might actually put the lid on initiative and drive and competitiveness,” Ziyad Al-Aly, a researcher at Washington University in St. Louis who has studied GLP-1s, told me. Lack of research is a problem here too, Al-Aly emphasized: The best evidence of this hypothetical effect is a preprint study that found that mice sought out their exercise wheel less after being injected with semaglutide.[Read: Ozempic is a brain drug]Some studies on the effects of GLP-1s in certain sports are now under way. WADA, for example, is funding a trial to test how semaglutide changes runners’ body composition and performance. But pharmaceutical companies are actively testing new types of weight-loss medications that may have different effects on muscle, as well as combinations of GLP-1s with other drugs meant to preserve strength. Some of those drugs, such as a class that overrides the body’s natural limit on muscle growth, are already banned by WADA. Every new weight-loss medication will complicate any tenuous understanding of how these drugs affect athletic performance.Determining whether a drug should be banned is not solely a scientific endeavor: WADA bases its decisions in part on whether the use of a drug violates “the spirit of sport,” which it defines as “the ethical pursuit of human excellence through the dedicated perfection of each Athlete’s natural talents.” Athletes earn our admiration because they work hard to perfect skills that most of us could never imagine having. We marvel at baseball sluggers because hitting a small ball traveling 90 miles an hour requires hard work; regularly hitting it 400 feet is that much harder. When a hitter takes an anabolic steroid, the wonder is largely lost.Williams became a tennis icon in part because of her relentless desire to compete. Even as a child, “she would run so hard to try to get to the ball, she’d fall,” Macci said. When she competed in the Australian Open while pregnant in 2017, she defeated every opponent who faced her, without dropping a set. Being 44, having two kids, and struggling with extra weight didn’t stop her from returning to professional tennis. Yes, she was probably lighter and quicker because she took a GLP-1. But a good comeback embodies the spirit of sport, too.