GLP-1 weight loss drugs are not currently banned in professional sports, but scientists are increasingly questioning whether they could provide athletes with a competitive edge beyond simple weight reduction. As high-profile athletes including tennis star Serena Williams publicly discuss using these medications, the sports world faces a new question: should weight loss drugs be classified as performance-enhancing substances ?

Could GLP-1 Drugs Give Athletes an Unfair Advantage?

The debate centers on how these medications work and what effects they produce beyond weight loss. GLP-1 receptor agonists like semaglutide (sold as Ozempic and Wegovy) and tirzepatide (sold as Mounjaro and Zepbound) mimic gut hormones that signal fullness, leading to substantial weight reduction. In one year, these drugs can produce 15 to 22 percent body weight reduction, results no previous weight loss medication came close to achieving.

However, recent research suggests these drugs do far more than suppress appetite. A study published in the Lancet found that weight loss accounts for only one-third of the cardiovascular benefits these drugs provide. They also reduce inflammation, improve metabolic health, and lower the risk of heart attacks and strokes through mechanisms scientists don't yet fully understand.

For athletes, these additional benefits raise important questions. Williams, who is a brand ambassador for Ro, a company that administers GLP-1 drugs, has publicly stated that her cardiovascular risk decreased by 19 percent, her joints improved, and her cholesterol improved while taking tirzepatide. She also noted that "I can pull moves I could, quite frankly, never do before".

"I wouldn't rule out the possibility that GLP-1s are somehow indirectly making the metabolic environment more efficient for exercise," said Daniel Drucker, an endocrinologist at the University of Toronto who pioneered research in GLP-1 drug development.

Daniel Drucker, Endocrinologist at the University of Toronto

Drucker explained that GLP-1 drugs improve blood flow to muscles and protect organ health through their role in decreasing inflammation, effects that could theoretically benefit athletic performance.

What Do Anti-Doping Agencies Think About GLP-1 Use in Sports?

Currently, GLP-1 weight loss drugs are not banned by the World Anti-Doping Agency (WADA), the international organization that sets standards for fair competition. To be classified as doping, a substance must meet specific criteria: it must have the potential to enhance performance, pose a health risk to athletes, or violate the "spirit of sport".

According to David Cowan, a world expert on drug detection and anti-doping at King's College London, GLP-1 drugs are not currently considered "unfair" or performance-enhancing by WADA. However, the agency is paying close attention. GLP-1 medications remain on WADA's monitoring list, which tracks substances that are not yet prohibited but warrant observation for potential misuse in sports.

The uncertainty stems partly from a lack of research. GLP-1 drugs have not been studied in elite athletes, making it difficult for scientists to determine whether they actually improve performance in this population. Massimo Mapelli, a cardiologist and exercise physiologist at the Centro Cardiologico Monzino in Milan, Italy, noted that "things are rapidly evolving and what we have considered normal until now is changing".

Where Could GLP-1 Drugs Create the Biggest Competitive Advantage?

One area where these drugs could be considered performance-enhancing is in sports with strict weight categories. In boxing and wrestling, athletes must meet specific weight limits to compete in their division. In these sports, using weight loss drugs could provide a direct advantage, similar to how diuretics, which are banned, allow athletes to become lighter.

For other sports, the picture is more complicated. Abbie Smith-Ryan, a professor of exercise physiology at the University of North Carolina at Chapel Hill, emphasized that exercise itself "outperforms the drug" at reducing inflammation. She also noted that the strongest inflammation-reducing effects from GLP-1 drugs appear in people with obesity or overweight, not in lean, already-fit athletes.

"If small doses of these drugs do turn out to meaningfully reduce inflammation in lean athletes, there could indirectly be a role in recovery, and potentially performance. We're just not there yet scientifically," Smith-Ryan explained.

Abbie Smith-Ryan, Professor of Exercise Physiology at the University of North Carolina at Chapel Hill

What Are the Real Risks for Athletes Using These Drugs?

Beyond the performance question, GLP-1 drugs carry documented side effects that could actually harm athletic performance. These include muscle loss, gastrointestinal issues, and, in rare cases, severe pancreas inflammation. Muscle loss is particularly concerning for athletes, since muscles are essential for speed, endurance, and injury prevention.

Research shows that the proportion of lean mass lost varies by drug. A meta-analysis found that approximately 35 percent of weight lost with semaglutide was lean mass, which includes muscle, water, and other non-fat tissues, compared with about 25.4 percent with tirzepatide. However, the same study noted that "muscle mass can be significantly preserved by integrating resistance training, adequate protein intake, and body composition monitoring".

Michael Joyner, a specialist in exercise physiology and fellow of the American College of Sports Medicine, suggested that if an athlete loses body fat while maintaining or gaining muscle through continued training, this could benefit them. In elite sports, he noted, "being able to leverage tiny margins" is extremely important, and losing a few kilograms can be "transformative to help people move around faster and improve their endurance".

How to Safely Use GLP-1 Medications if You're an Athlete

• Monitor weight loss velocity: Losing more than roughly 2 kilograms per week puts athletes in the highest-risk group for side effects like muscle loss and hair shedding, so gradual weight loss is preferable.
• Combine with resistance training: Integrating strength training, adequate protein intake, and regular body composition monitoring can significantly preserve muscle mass during weight loss.
• Consult with sports medicine professionals: Athletes should work with doctors who understand both their sport and GLP-1 medications to ensure safe use and monitor for performance impacts.

The bottom line, according to Daniel Drucker, is that the scientific evidence remains incomplete. "Until then we just have to, I think, sit on the fence and say there's no data to suggest they're performance-enhancing, but absence of evidence is not evidence of absence," he stated.

As more athletes consider using GLP-1 drugs for weight management, both sports organizations and the medical community will need to develop clearer guidelines. For now, these medications remain a gray area in sports, monitored but not banned, with their true performance implications still unknown.