By Alex Janin

Amanda Rodriguez felt exceptionally proud as she ran the Chicago Marathon last fall. She also felt a touch weighed down.

With other races on the horizon, she decided to go back on tirzepatide, the active ingredient in popular diabetes and weight-loss drugs Mounjaro and Zepbound. She had used it before to take off some excess weight. Now she wanted to lose more to improve her running performance.

"My body just feels stronger," says Rodriguez, 30, who has since lost 20 pounds while maintaining her diet and training schedule. She has also shaved a minute from her 5-kilometer time and completed her first ultramarathon.

Since Ozempic burst into the culture, medical researchers have discovered the drug and its cousins might offer wide-ranging health benefits, including curbing addictions and battling the aging process.

Now a burgeoning community of runners, cyclists and other sports and exercise enthusiasts are taking the weight-loss drugs in the hopes of gaining a performance edge. For members who are on the medications, gym operator Equinox has even created a personalized "GLP-1 protocol" training program that focuses on muscle-building and retention.

How far the experimentation goes is unclear, but it has caught the attention of the World Anti-Doping Agency. Last year, it added semaglutide, Ozempic's active ingredient, to a list of substances it monitors to find potential patterns of misuse.

Some health experts also have concerns: The drugs come with side effects that pose potential risks, such as too much appetite suppression for fuel-burning athletes. More research is needed on their use among healthy, fit people, they say.

Yet these medicines could offer athletes in weight-sensitive sports a potential advantage, and might also carry performance benefits unrelated to weight loss, such as improving endurance and speeding up recovery times, doctors and researchers say.

Dr. Richard Isaacson, a preventive neurologist, says he has recommended microdosing -- taking a fraction of the regular dose -- for some patients who are eager to optimize health and physical performance. One is a former Olympic gold medalist.

"We tried to see what was the minimal dose that he could tolerate without losing any more weight," says Isaacson of the former Olympian, who had already been on a new diet and nutrition regimen. Over months, the athlete gained muscle, improved his VO2 max, a measure of aerobic capacity, and lowered his risk for neurodegenerative disease. "Everything about his everything improved."

Microdosing experiments

Isaacson says he has experimented with various doses of a GLP-1 himself, hoping it might improve his LDL cholesterol levels and help him feel a little lighter in his running shoes.

But a standard starting dose of 2.5 milligrams of Zepbound curbed his hunger to the point that it was difficult to eat enough to maintain his exercise regimen. Already at a healthy weight, he lost more pounds than he wanted to.

After reducing the dosage, Isaacson arrived at 0.75 milligrams as a "sweet spot" with no negative side effects. Test results, running logs, and body composition analyses over the next year show many of his health markers went from good to great: His cholesterol, muscle mass and VO2 max improved. He stopped craving Girl Scout cookies. And this January, he ran his best half-marathon in 15 years -- 10 minutes faster than his last one.

The question, he says, remains: "Is that performance-enhancing, or is it health optimization? I think that's a gray area."

Microdosing isn't sanctioned by the FDA or the drugmakers, and no clinical trials have supported its safety or efficacy. A spokesperson for Novo Nordisk, which makes Ozempic and weight-loss drug Wegovy, describes microdosing as a misuse of its products, while Eli Lilly, which makes Mounjaro and Zepbound, says microdosing could raise safety risks.

Mixed results

Some athletes say they aren't deterred by less-than-satisfactory results. Jane Anderson, a 56-year-old triathlete, is training for her 14th Ironman, which includes a 2.4-mile swim, 112-mile bike ride and a marathon-length run.

In about six months on Wegovy, she lost a little under 5 pounds. Fatigue and low blood sugar made it difficult to keep up with her training schedule of 12 to 18 hours a week, and she found herself taking hourlong naps in her car before getting into the pool.

She plans to try a different brand at some point -- unless it is banned.

"This drug is one of those things that when you take it, you finally have hope," she says. "You'll have a faster swim, you'll have a faster ride, you'll certainly climb hills better."

If the World Anti-Doping Agency finds semaglutide does two of three things -- enhances performance, poses a health risk or violates the "spirit of the sport" -- it could end up on its banned list.

Making that determination is complex, says Matt Fedoruk, chief science officer at the U.S. Anti-Doping Agency. A long-distance runner on semaglutide, for instance, might lose too much lean muscle and struggle to eat enough to fuel hours of effort, he said. The drug might help an athlete in a sport such as boxing or wrestling quickly move to a lower weight class.

For lean athletes just looking for an edge, lifestyle changes are the better bet, said Dr. Kathryn Ackerman, the head physician for U.S. Rowing.

"I would get back to some of the basics with training and talk about how we optimize your nutrition, your recovery, your training plan," says Ackerman, a former national team lightweight rower. "I'm not a big fan of hacks."

John Jakicic, a fellow of the American College of Sports Medicine who researches physical activity and weight management, says the loss of lean body mass -- including muscle -- that accompanies weight reduction with these medications can be problematic, especially for leaner athletes. In a study he is conducting, some nonathlete patients who might have previously been able to push to 80% of their maximum effort might now only reach roughly 60% or 70% on GLP-1s, he adds.

"We can't push them like we could push an athlete," says Jakicic. "Just because you can get to a weight doesn't mean you're going to perform at that weight."

Matt Jett, a St. Louis-based lawyer who lifts weights, plays roller hockey and has raced in hourslong dirt-bike competitions, said occasional tiredness is worth the results. The 39-year-old finds it more difficult to exercise on the first day or two after his tirzepatide shots. But he says losing about 30 pounds helped him eventually win a race in his age and skill group.

"I went from finishing toward the back of my age group class and being really, really exhausted at the end of the races to finishing feeling strong," Jett says.

Write to Alex Janin at alex.janin@wsj.com

(END) Dow Jones Newswires

April 26, 2025 21:00 ET (01:00 GMT)

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