GLP-1 for Sports Performance

GLP-1 Agonists as Performance Enhancers

While researching content for our podcast (Dr Schwartz and Mr Power), I discovered that  GLP-1 agonists (such as Zepbound, Ozempic, etc.) aren't on the World Anti-Doping Agency's (WADA) list of banned substances. Initially I was surprised at this, but I suppose I shouldn't be.

For those who don't know, WADA is the agency responsible for deciding which drugs and agents are banned in sporting events such as the Olympics. Why am I surprised that a drug class developed to treat diabetes, that found a use in weight management isn't on a list concerned with sport performance? Also, aren't these drugs associated with significant losses in lean body mass and wouldn't that hurt sports performance? These are fair questions, so let me explain. 

First I should clarify that I'm not giving advice on drug use, medical or recreational. Instead, I'm making a prediction. My prediction is that athletes in sports with weight divisions and those where power-to-weight ratio is critical will start using GLP-1 agonists as a performance enhancing drug (PED).  

GLP-1 Muscle Loss Fallacy

I haven't seen others make an argument along these lines yet and I think I know why. During the Semaglutide Step 1 Trial  (Semaglutide being the active compound in Ozempic) the experimental group receiving Semaglutide lost ~15.0% of their body-mass over 68 weeks. This is old news by now. The part that's been getting undue attention is that they also lost 9.7% of total lean body mass (5.36 kg). This amounts to 35% of the total weight loss being lean mass. 

Losing 35% of your weight as lean mass might seem alarming. This becomes even more alarming if you confuse "lean mass" with "muscle mass". However, this is almost exactly what we should expect when talking about significant weight loss, and a 15% reduction in bodyweight is definitely significant. So what is lean mass then?

Lean mass does not mean muscle mass. Lean mass is everything in your body that isn't adipose tissue ("fat"). Bone, brain, visceral organs, skin, water, muscle, and even food in your intestines will all register as "lean mass". Whenever you lose a significant amount of weight, you lose lean mass. For example, your intestines will shrink as you lose weight. You're eating less, so you need less intestine to do the work of digesting. 

But it turns out 35% is within the normal range for the proportion of lean mass weight people lose when they lose significant weight. This really shouldn't be surprising since we've had this estimate since 1983 (Brown et al.), with similar estimates going back as far as the 1950's (Minnesota Starvation Experiment). Interestingly, this number does seem to change when people are leaner. When people are already lean, the proportion of lean mass lost tends to increase.

So if this 35% lean mass number isn't surprising, why is everyone acting so surprised? In short, too many people (particularly fitness industry types) don't do their homework. I'm actually kind of disappointed with the number of people with a research background who are also acting like patients should be uniquely concerned about lean mass loss while taking GLP-1 agonists. 

If this hasn't convinced you, the following case studies might. A case study followed 3 patients with overweight and obesity taking GLP-1 agonists (Tinsley and Nadolsky, 2025). Unlike the Step 1 study, participants all engage in exercise regimes that included strength training. Two of the participants actually increased lean mass, while one lost 8.7% lean mass (not muscle mass). Notably, the exercise regimes were described as "light", and were not representative of a progressive challenging strength-training regime. 

Some readers might object to leaning on a case-study of three individuals as a source of evidence. This is hardly an appropriate sample size and there's no control group. However, since there was never any reason to think that lean mass loss was a concern I think it's still informative. Further, of my clients that I've known to be taking GLP-1 agonists, I haven't seen any lose in strength associated with the notable loss in body-mass. While strength is obviously a loose proxy for muscle mass, it's also much more important than muscle-mass for health. 

To summarize, I think that the misunderstanding that GLP-1 agonists have a unique negative effect on lean mass coupled with peoples conflation of lean mass with muscle mass is why we're not seeing athletes jumping on GLP-1 agonists as PED's. 

What About Athletes?

Why do I consider GLP-1 agonists a potential performance enhancing drug? After all it doesn't seem to have a direct impact on muscle size of performance (good or bad). I see two primary use-cases. Making weight, and improving strength to power ratio.

Sports like weightlifting, powerlifting, and combat sports all have weight divisions. So athletes need to weight less than some threshold weight. For pretty much all of these sports there's an advantage to being as powerful and muscular as possible. In order to be as strong and powerful as possible, while staying below your division's threshold, it pays to be lean. 

Unfortunately staying lean is difficult, even for many athletes. So athletes frequently live and train heavier than their competitive weight, then diet down in the weeks leading up to competition. Drugs that make it easier to stay closer to competition weight, or push down to your final weight provide a distinct advantage. The common practice of rapidly dropping weight before competition can result in low muscle glycogen, hampering performance.

The second use-case for these drugs as performance enhancers are sports where a high power to weight ratio is a significant advantage. Many track and field events fall into this category, with sprinting being an easy one to understand. Every extra gram you carry on your body, is an extra gram you have to accelerate down the track. So minimizing dead weight can be a significant advantage. In fact, a sprinter might even benefit from losing lean mass (or even some muscle) if that loss in mass is greater than the relative loss in power. 

Because losing muscle raises the spectre of potential power loss, this is something that the athletes would want to titre. An athlete and coach would need to know beforehand (through trial and error) how much weight loss optimizes performance and how much hampers performance. 

Final Thoughts

I'm not trying to make recommendations about using GLP-1 agonists as performance enhancing drugs; and I'm not just saying that as a weak attempt to minimize liability. These really are medications whose use should be monitored by a physician. But I've been around sports long enough to recognize how these might (and probably will) be used by athletes to eke out an advantage. 

I also think that this opens up the possibility to better manage the long-term health of super-heavyweight athletes, and athletes in events where absolute body-mass is pursued at the expense of athlete health. For example, football linemen, shot-putters, super-heavyweights in Weightlifting and Powerlifting all have history of chasing overall size at all costs. I think that re-thinking our approach to these athletes' health is long overdue and likely the topic of a future podcast and article.

For now WADA seems content to observe how these drugs are used, but I wouldn't be surprised if they ended up on their based substance list. Until then, I'll definitely be watching the issue with interest.

Citations

Wilding et al., Once-Weekly Semaglutide in Adults with Overweight or Obesity. N Eng J Med. 2021 Mar 18;384(11):989-1002

M R Brown, et al. A high protein, low calorie liquid diet in the treatment of very obese adolescents: long-term effect on lean body mass, Am J Clin Nutr. 1983, Jul;38(1):20-31

Minnesota Starvation Experiment

Tinsley et al. Preservation of lean soft tissue during weight loss induced by GLP-1 and GLP-1/GIP receptor agonists: A case series. SAGE Open Med Case Report. 2025, Oct 16;13:2050313X251388724