Weight loss drugs are affecting Serena Williams’s Wimbledon – is it time for a ban?

The undeniable tennis GOAT, Serena Williams, returned to Wimbledon this week after a nearly four-year hiatus from professional sport.

The 44-year-old athlete always turns heads – she’s the only player to have simultaneously held Olympic gold and all four major Slam titles in both singles and doubles, after all. While her long-awaited Wimbledon comeback ended in defeat, her first Grand Slam singles match since stepping away from the tournament was much more competitive than expected.

And with this most recent comeback, she attracted as much attention for the debate surrounding her 2.5st (34lb) weight loss as she did for her tennis. She may have been beaten by Australian rising star Maya Joint on Tuesday, but, as Flo Clifford wrote in her match review, her “champion’s desire” was still on show.

Williams is the latest famous face to embrace GLP-1s – the collective name for a set of drugs used to treat diabetes and obesity – and has credited their use for her return to Wimbledon. It’s sparked the mother of all debates when it comes to the application of these medications in sport. Should they even be allowed?

Williams, at least, hasn’t tried to hide or deny the part that weight loss injections have played in her transformation. Unlike plenty of A-listers, she’s been transparent about the process, making her the first active elite athlete to “come out”, as it were, about her use of this type of weight loss medicine. More than that, she’s even started shelling for Ro – a direct-to-patient healthcare company for which Williams’s husband, Alexis Ohanian, serves as a board member and investor – as one of its “celebrity patient ambassadors”.

“I feel great,” she told People of her weight loss after using tirzepatide (branded as Mounjaro and Zepbound) last year. “I’m more active. My joints don’t hurt as much. I just feel like something as simple as just [bending] down is a lot easier for me, and I do it a lot faster. I feel like I have a lot of energy and it’s great.”

Williams returned to Wimbledon after a four-year hiatus but went out in the first round (Reuters)

But as positive and refreshing as Williams’s story might seem, it has opened up a fierce debate on the use of GLP-1s in sporting competitions.

These drugs were initially created and approved for people with type 2 diabetes; Ozempic, a brand of semaglutide, is licensed specifically for this demographic. Soon enough, new medications targeting weight loss hit the market, including Mounjaro (tirzepatide), Wegovy (semaglutide) and Saxenda (liraglutide).

Widespread use has been relatively recent; in the UK, it started in late 2023 to early 2024, primarily driven by private prescriptions; recent data revealed that an estimated 8.25 million people in the UK have either taken, are taking or are considering taking GLP-1 weight loss medications,

We are still learning about the health impacts, both positive and negative, of taking these drugs long term, and there has been far too little research into their use in sports to know whether they could potentially “enhance” an athlete’s natural performance (or, indeed, detract from it).

We want to see whether we detect patterns of abuse of this drug or this class of substances in sport

Dr Olivier Rabin, senior director at WADA

Right now, GLP-1s are permitted in sport across the board, but the World Anti-Doping Agency (WADA) has put them on its official watchlist, actively monitoring their use by athletes to determine if they should be banned in the future.

“It is our understanding that the WADA List Expert Advisory Group are collating further evidence about the use of glucagon-like peptide-1 receptor agonists in sport to determine whether they should be prohibited,” says the UK’s Anti-Doping body, UKAD.

“We want to see whether we detect patterns of abuse of this drug or this class of substances in sport,” Dr Olivier Rabin, WADA’s senior director of science and medicine, told Sky News earlier this year.

“So we keep an eye on them because there’s been a change in paradigm in the way weight can be controlled because of those drugs. There is an interest from all sides, from the performance-enhancing aspects and health protection of the athletes with this class of substances [and] will they end up being on the [banned] list.”

WADA is currently funding a trial looking at how semaglutide changes runners’ body composition and performance.

In the meantime, professionals have expressed wildly varying attitudes towards GLP-1s in sport. “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 The Atlantic.

The World Anti-Doping Association is considering banning GLP-1s like Mounjaro from professional sport (AFP via Getty)

Meanwhile, Michele Verroken, the director of Sporting Integrity, an anti-doping consultancy, and the former head of ethics and anti-doping for UK sport, called the use of these drugs in competitive sport “very controversial”.

“A drug that can help you lose weight should certainly be restricted for weight category sports like boxing or weight lifting,” she told BBC Radio 4’s Today show, adding that their use by athletes in sports like cycling “where there’s a power to weight ratio, so you’re trying to reduce your weight but maintain your power to optimise your performance, might be really encroaching on what we regard as a likelihood to enhance performance.”

Substances are banned by WADA if they meet at least two of three criteria: Does it enhance performance? Is there a potential health risk for the athlete? And does it violate the “spirit” of sport? “I think we could see two of these categories met and [GLP-1s] added to the list, certainly for some sports,” said Verroken.

Relatively few drugs are currently banned in some sports but not others. One example is beta blockers, which are prohibited in sports including golf, archery, darts, shooting and car racing, but not in football and elsewhere. It could be that GLP-1s are specifically forbidden in weight category sports; additionally, national cycling bodies have already discussed banning them even if WADA decides not to.

But what about the other side of this? Could using GLP-1s actually hinder athletic performance? Using a weight loss injection or pill could certainly impact strength unless users are careful; around 25 per cent of the weight that GLP-1 patients lose is lean mass, according to one meta-analysis published last year.

A drug that can help you lose weight should certainly be restricted for weight category sports

Michele Verroken, director of Sporting Integrity

In one Reddit thread discussing the use of GLP-1s in cycling, many commenters argued that weight loss drugs were the “opposite of doping”: “Don’t be shocked to lose 20+ per cent of your power while you’re on it,” wrote one. “I’d consider it the reverse of performance-enhancing,” said another. “Yes, you lose weight, but you lose muscle, and there are no indications based on studies that GLP improves physical performance in any way.”

A third added: “I know cyclists who have taken them. Their performance was non-existent after like 23 months. Not worse, like, zero. You cannot fuel, and you cannot train.”

The argument also took in the well-documented side effects associated with taking GLP-1s, which include sickness, nausea, diarrhoea and constipation: “A friend tried this and would literally vomit after taking gels.”

But a less tangible yet even more powerful factor could also potentially harm sporting performance. GLP-1s are believed to dampen dopamine signalling in the brain, which is why they are so effective at quieting food noise, as well as potentially being a ground-breaking cure for addiction.

Some believe this same mechanism might also curb motivation, drive and competitiveness; research is scant, but one preprint study found that mice ran on their exercise wheel less after being injected with semaglutide.

In the case of Williams and her recent return and subsequent defeat, it is perhaps notable that US tennis writer Ben Rothenberg described her as seeming “much less fiery” and with “less hunger and need to be the best than there was before”.

It might simply be down to being at a different stage in her life and career: “She seems like she’s here almost with a summer fling for tennis – here for a good time, not a long time,” Rothenberg told Radio 4. The tennis star herself admitted to Clare Balding pre-match that she was yet to experience any butterflies. A consequence of this being her swansong singles competition, or of GLP-1s quelling her innate need to win? The jury’s still out, and will be watching closely when Serena is joined by sister Venus for their first-round women’s doubles match on Thursday.