LONDON: GLP-1-based weight-loss medicines have transformed the treatment of obesity and helped many people achieve significant weight loss, but their growing use among athletes has sparked a new debate over whether the drugs could also influence sporting performance.
The issue has received renewed attention following comments from tennis legend Serena Williams, who discussed using a GLP-1 weight-loss medicine after struggling to lose weight following the birth of her child. Williams said that despite spending extensive hours training, she found it difficult to reduce her weight.
In an interview, Williams said she had used tirzepatide, a medicine sold under brand names including Zepbound and Mounjaro. Tirzepatide is among a growing group of medicines designed to help people lose weight by reducing appetite and increasing feelings of fullness.
The drugs have become increasingly popular because of their ability to produce substantial weight loss. GLP-1 medicines mimic the effects of a naturally occurring gut hormone that helps regulate appetite and food intake. Tirzepatide also acts on another hormone pathway known as GIP.
For athletes, however, the question is more complicated. Competitive sport has strict rules surrounding substances that could provide an unfair advantage, and anti-doping organisations regularly assess medicines and compounds for their potential effects on performance.
The central question is whether weight loss caused by GLP-1 medicines should itself be considered a performance advantage, or whether the drugs should simply be viewed as medical treatments that can help athletes achieve a healthier body weight.
There is currently no clear scientific evidence that GLP-1 drugs directly enhance athletic performance in the way traditional performance-enhancing substances can. However, researchers are examining whether the physical changes caused by the medicines could indirectly affect sporting ability.
For some athletes, losing excess body weight could potentially make movement easier and reduce the physical demands placed on the body. In sports such as tennis, running or cycling, body weight can influence endurance, agility and energy expenditure.
At the same time, rapid or substantial weight loss can create challenges for athletes. Losing weight can involve reductions in muscle mass as well as fat, particularly if protein intake and resistance training are not carefully managed. For elite competitors, preserving muscle strength and maintaining adequate nutrition are essential.
Another concern involves energy availability. Athletes need sufficient calories and nutrients to support intensive training, recovery and competition. Appetite-suppressing medicines could make it more difficult for some athletes to consume enough food to meet those demands.
This creates a complicated balance between potential health benefits and sporting requirements. An athlete who has obesity or another medical condition may experience clear health improvements from medically supervised weight-loss treatment, while the same treatment could raise questions about nutrition and performance in an elite sporting environment.
The debate has also intensified as high-profile athletes and celebrities openly discuss their use of GLP-1 medicines. Serena Williams’ comments have brought additional attention to the issue at a time when interest in these drugs is expanding well beyond traditional medical settings.
Whether GLP-1 medicines should eventually be classified as performance-enhancing substances will depend on scientific evidence and decisions by sports governing bodies and anti-doping authorities. At present, the evidence does not establish that these medicines directly provide athletes with an unfair competitive advantage.
Experts are therefore likely to continue examining their effects on body composition, muscle strength, endurance, recovery and training capacity. More research will be needed to determine whether the indirect effects of significant weight loss translate into meaningful advantages in different sports.
For now, the distinction between medical treatment and performance enhancement remains central to the debate. GLP-1 medicines can help people lose weight and improve aspects of their health, but whether those benefits amount to a sporting advantage is a much more complex question.
As professional athletes increasingly use weight-loss medicines under medical supervision, sports organisations may face growing pressure to establish clear guidance on their use. The challenge will be to protect fair competition while ensuring athletes with legitimate medical needs can access appropriate treatment.
