For marathon runners in their 50s like Keri M, the intersection of endurance training and weight-loss medication has proven difficult. After qualifying for the 2024 Bank of America Chicago Marathon, Keri faced her first race while on a 2.5mg starting dose of tirzepatide, a GLP-1 drug sold under brands like Mounjaro and Zepbound. The experience was physically taxing; she reported feeling so sick during a half marathon that she struggled to consume essential energy gels, a reaction she now attributes to starting at an inappropriately high dose. This feeling couldn’t be chalked up to inexperience. Keri, who asked us to omit her full name due to the sensitive subject matter, has completed dozens of half marathons and four full marathons. One of the eight world marathon majors, she ran the 2024 Philadelphia marathon fast enough to earn a coveted spot in this year’s Bank of America Chicago race. In hindsight, wishes that she had started at a lower dose, keri had a “severe” reaction to the 2.5mg dose and. Others argued that her openness may help reduce the shame surrounding GLP-1s. Runners relate to her journey, yet despite the pushback. He started gaining weight, around the age of 41. “No matter how hard I trained, no matter how much I tracked my macros and stayed on plan, I just kept gaining weight,” he said. He noticed Williams had a similar story of turning to a GLP-1 because she couldn’t reach her desired physique through diet and exercise. A tip he saw on Reddit, steve cut his 2.5mg dose in half after four weeks.
Usage of these drugs for weight management has surged, rising from 3% to 11% over the last two years. A 2026 cohort study indicates that non-FDA-approved use is now 15 times higher than it was five years ago, with 35% of current users falling outside the clinical criteria for being overweight by BMI standards. Meghann Featherstun, a sports dietitian in Ohio, notes that these medications are now significantly more accessible than upon their initial release, as prescription requirements have eased. The number of people taking GLP-1s to lose weight has grown from 3% to 11% in the past two years. A decorated female tennis player, became a spokesperson for Ro, a telehealth company that sells GLP-1s, it opened up a debate over who should take these drugs and if they have a place in sports, when Serena Williams. But now required multiple breaks and spiked his heart rate higher than usual, five miles usually came easy. He can now train without a heart-rate spike. “I don’t feel as exhausted any more,” he said.
Expert opinions on combining these drugs with high-intensity training remain divided. Heidi Skolnik, a fellow of the American College of Sports Medicine, suggests that performance is possible only if the athlete can adequately maintain hydration and caloric intake to fuel their efforts. However, she warns that if an athlete cannot manage these basic physiological needs, they risk compromising their overall health. Some experts, such as Heidi Skolnik, a fellow of the American College of Sports Medicine and author of Your GLP-1 Game Plan, believe it’s possible to run longer races while taking GLP-1s.
The physical impact on runners can be profound. For many, the side effects—nausea, loss of appetite, and fatigue—are immediate. Steve, a 44-year-old from Oregon, struggled with sudden heart-rate spikes during training after beginning a tirzepatide compound in July 2026. While he eventually mitigated these issues by cutting his 2.5mg dosage in half, he noted that his weight loss progress stalled. Dr. Melanie Jay of the NYU Grossman School of Medicine explains that GLP-1s can induce a resting heart rate increase of two to 10 beats per minute, which can intensify during athletic exertion. Steve, a 44-year-old from Oregon, who asked to be identified by only his first name because of the deeply personal topic, has always considered himself active.
Nutritional experts emphasize the heightened risk of Relative Energy Deficiency in Sport (REDs) for those on these medications.
Claire Shorenstein, a board-certified sports dietitian, cautions against using GLP-1s while actively training for endurance events. Because the drugs suppress appetite, they often trap athletes in a state of low energy availability, which can lead to reduced bone density, immunity issues, and in women, hypothalamic amenorrhea. Keri, the Chicago-bound marathoner, confirmed she faced a definite risk of REDs due to her inability to fuel correctly during the program.
Some athletes, like Texas-based Kylie Keeton, have attempted to navigate these challenges by microdosing or adjusting training schedules, but the results are often discouraging.
Keeton, who lost 170 pounds naturally before experiencing weight fluctuations during training, found that the persistent nausea made maintaining her mileage impossible, eventually leading her to quit the drug entirely.
Similarly, while some, like a participant who improved their Sydney Marathon time by three hours after an initial bout of illness, eventually adapt, experts like Emily Lundstrom argue that performance-minded athletes should ideally avoid these medications until their competitive seasons conclude.
Ultimately, clinical research regarding the long-term interaction between GLP-1 medications and high-mileage running remains sparse. While some suggest timing doses after long runs or lowering dosages to manage symptoms, the consensus among many dietitians is that the medication’s side effects frequently undermine the physical demands of distance running. For many, the high cost and debilitating physical reactions make the combination a precarious trade-off that may not be sustainable for peak athletic performance. He went for casual runs, boxed and lifted weights, even when he wasn’t training for a long-distance race.
