GLP-1 in Sports: Medical Breakthrough, Performance Tool, or Emerging Risk?

Weight Loss and Improving Performance

The relevant question is not only “How much weight was lost?” but “What tissue was lost, and what happened to performance?” A 2024 network meta-analysis of 22 randomized trials found that GLP-1-based treatments reduced fat mass but also reduced lean mass; approximately 25% of total weight loss was lean tissue⁽¹⁾.

The athlete should not interpret this to mean that 25% of the weight loss is necessarily contractile muscle, because DXA-derived lean mass includes body water and non-fat tissues. Nevertheless, the signal is important for this study. In a STEP 1 substudy, semaglutide reduced body mass by 15.0%, fat mass by 19.3%, and lean mass by 9.7% over 68 weeks⁽²⁾. In the SURMOUNT-1 substudy, tirzepatide reduced body mass by 21.3%, fat mass by 33.9%, and lean mass by 10.9% over 72 weeks⁽³⁾. Both studies involved people with overweight or obesity, not athletes, and neither established the consequences for sprinting, strength, power, repeated high-intensity efforts, or injury risk.

A better fat-to-lean ratio may be advantageous only if muscle function, training quality, and recovery are preserved (see table 1). Rapid weight loss accompanied by reduced force production, depleted glycogen stores, or limited training availability may worsen rather than improve performance.

Table 1: Potential benefit versus practical concerns of GLP-1 use in athletes

The Athlete-Specific Risks

Nausea, vomiting, diarrhea, constipation, abdominal discomfort, and delayed gastric emptying are well-recognized adverse effects. In daily life, these may be manageable; however, during heat exposure, travel, double training sessions, or competition, they can disrupt carbohydrate delivery, hydration, and recovery. Hypoglycemia is usually uncommon when these agents are used alone, but the risk changes when they are combined with insulin or insulin secretagogues.

A deeper concern is chronic under-fueling. Athletes whose hunger is markedly reduced may struggle to consume sufficient total energy, carbohydrates, and protein. Low energy availability can impair endocrine and reproductive function, bone health, immunity, protein synthesis, cardiovascular health, and psychological well-being while compromising training response and performance. In susceptible athletes, this may contribute to Relative Energy Deficiency in Sport (REDs)⁽⁴⁾. Weight-category and aesthetic sports increase the risk of rapid loss, disordered eating, and secrecy.

Product-specific contraindications and warnings are also important. These include severe gastrointestinal reactions, gallbladder disease, pancreatitis signals, kidney injury secondary to dehydration, and contraindications related to medullary thyroid carcinoma or multiple endocrine neoplasia type two. A drug that is appropriate for one athlete may be unsuitable for another athlete.

Managing Risks

Where a genuine clinical indication exists, management should be integrated rather than left to the prescriber. Sports physicians and dietitians should establish baseline health, medication, and eating disorder history; monitor gastrointestinal symptoms, hydration, and weight loss rate; and track body composition alongside strength, power, training quality, recovery, injuries, menstrual function, and other REDs indicators.

Resistance training and adequate protein intake are rational strategies to protect lean tissue, although specific trials in athletes taking GLP-1 drugs are lacking(5). In adults with obesity, supervised exercise combined with liraglutide produced greater improvements in body fat percentage and cardiorespiratory fitness than either approach alone⁽⁶⁾. This supports exercise as an essential companion to treatment, not as proof of an ergogenic drug effect.

“A deeper concern is chronic under-fueling.”

Practically, athletes may need smaller, more frequent meals; deliberate carbohydrate intake before and during demanding sessions; protein distributed throughout the day; and an individual hydration plan. Dose escalation and competition schedules should be coordinated with the treating clinicians. Persistent vomiting, inability to fuel, rapid functional decline, or emerging REDs features should prompt a prompt reassessment.

Permitted, but Watched, by WADA

GLP-1 receptor agonists are not prohibited under the 2026 World Anti-Doping Agency (WADA) Prohibited List. Semaglutide and markers of other GLP-1 analogs are included in the 2026 monitoring program⁽⁷⁾. Monitoring is surveillance; i.e., detection does not constitute an anti-doping rule violation.

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WADA may prohibit a substance if it meets at least two of the following three criteria: potential to enhance performance, actual or potential health risk, and violation of the spirit of sport⁽⁸⁾. The case for prohibition is that GLP-1 drugs could facilitate aggressive weight manipulation, provide an advantage in weight-sensitive sports, and carry health risks when misused. The counterargument is stronger at present: there is no robust evidence of direct performance enhancement in healthy athletes; the appetite and lean mass effects may impair performance; and athletes may have legitimate medical indications.

Questions before an athlete uses a GLP-1-based drug 

•    Is there a clear, documented clinical indication?
•    Who prescribes the drug and coordinates it with the sports medicine team?
•    Are body composition, strength, power, and training quality being monitored, in addition to body weight?
•    Can athletes still meet their energy, carbohydrate, protein, and hydration requirements?
•    Are gastrointestinal symptoms interfering with training, travel, or competition?
•    Are menstrual function, bone health, mood, recovery, or injury patterns changing?
•    Has the exact medication been checked against the current WADA list?

Based on current evidence, targeted monitoring, education, and medical oversight are more defensible than a blanket ban. This position should remain open to revision as athlete-specific prevalence, performance, and safety data emerge. Athletes must still check the exact product before use, as formulations and anti-doping rules can change.

“GLP-1 receptor agonists are not prohibited...”

The Final Whistle

GLP-1-based drugs are powerful medicines that are not simple appetite suppressants or proven performance enhancers. They may improve health and training capacity in athletes with a valid clinical indication, but intentional weight loss can include lean tissue, and appetite suppression may undermine the fueling on which performance depends. The key sporting principle is therefore not “lighter is better,” but “health, function, and performance must be protected.” Use should be medically justified, openly coordinated with the sports medicine team, and monitored beyond the scale reading.

References

1. Metabolism. 2025;164:156113. 
2. J Endocr Soc. 2021;5(Suppl 1):A16-A17. 
3. Diabetes Obes Metab. 2025;27:2720-2729. 
4. Br J Sports Med. 2023;57:1073-1097. 
5. Diabetes Care. 2024;47:1718-1730. 
6. N Engl J Med. 2021;384:1719-1730. 
7. World Anti-Doping Agency. The 2026 Monitoring Program. 2025. 
8. World Anti-Doping Agency. The Prohibited List: criteria for including substances and methods.