Could a drug designed for weight loss help athletes perform better?

GLP-1 weight-loss drugs can reduce weight and improve health, but could they also boost athletic performance? Scientists say the evidence is unclear, but there is a growing debate around whether they could be considered performance enhancing.

"The one opponent I could not defeat is the weight," Serena Williams said on Oprah Winfrey's podcast last year. "I literally was working eight hours a day in the gym training and I never could lose an ounce. In fact, I feel like I may have even gained weight," she said.

In the interview, she explained she began taking a GLP-1 weight loss drug after struggling to lose weight after her child was born. In an interview with Vogue, she said the drug in question was tirzepatide (which is sold under brand names Zepbound and Mounjaro). Williams is paid to be a brand ambassador for Ro, a company that administers the drugs, and her husband, Alexis Ohanian is an investor in the company.

It's one of several drugs on the market that suppress appetite and can lead to substantial weight loss. The drugs work by mimicking the gut hormone GLP-1 and in the case of tirzepatide, also GIP – both are hormones that make us feel full.

In sports, it's long been the case that any substance that gives you an edge is heavily scrutinised by opponents, spectators and anti-doping agencies. As she returns to professional tennis, Williams's decision to take a GLP-1 weight-loss drug has led to questions about whether they could improve athletic performance or are a legitimate way for an athlete to lose weight and improve their health. But should they be considered performance enhancing?

What is considered doping?

To be classified as doping in sports, a substance needs to meet specific criteria, explains David Cowan, a world expert on drug detection and anti-doping at King's College London, UK. They need to have the potential to enhance performance, have the potential to risk the health of the athlete or they violate the "spirit of sport".

While weight-loss drugs are not currently banned in professional sports, Cowan says doping agencies are paying close attention. GLP-1s remain on the World Anti-Doping Agency's (Wada) list of drugs to monitor. "The Monitoring Program includes substances which are not on the prohibited list, but that Wada wishes to monitor in order to detect potential patterns of misuse in sport," a spokesperson told the BBC.

With that in mind, weight-loss drugs are not currently considered "unfair" or performance-enhancing by Wada, says Cowan.

One reason for the uncertainty is that GLP-1 drugs have not been studied in elite athletes, says Massimo Mapelli, a cardiologist and exercise physiologist at the Centro Cardiologico Monzino in Milan in Italy. "Things are rapidly evolving and what we have considered normal until now is changing," he says.

As research develops, there are several ways scientists and sports organisations will be analysing how weight-loss drugs could affect athletes. One of the most direct ways could be in sports where there are strict weight categories.

In boxing and wrestling, for instance, athletes compete in weight categories and must meet the required weight limit to compete. In those sports, weight-loss drugs could be considered doping, says Mapelli. "You're essentially taking a drug that could give you an advantage," he says.

For similar reasons, the use of diuretics – drugs that cause the body to pass more urine and therefore make athletes lighter – are banned. They can also be used "to flush previously taken prohibited substances," Wada state.

Benefits beyond weight loss

Scientists have increasingly realised that the drugs affect the body beyond weight loss. GLP-1 drugs have been found to reduce inflammation, improve metabolic health and reduce the risk of heart attacks and strokes, with weight loss only accounting for one-third of the reduced cardiovascular risk, according to a recent Lancet study.

In other words, they can improve an individual's heart health independent of weight loss, but scientists don't know why.

Daniel Drucker, an endocrinologist at the University of Toronto, Canada, who was involved in pioneering research in........

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