Marathon runners are increasingly navigating the complex intersection of endurance training and the use of GLP-1 receptor agonists, such as tirzepatide. For many, including a marathoner in her 50s identified as Keri M, the reality of training while on these medications has proven physically taxing. After securing a spot in the 2024 Bank of America Chicago Marathon—a world major—through a strong performance in Philadelphia, Keri faced a difficult experience. Taking her initial 2.5mg dose of tirzepatide just a week before a race, she suffered from severe nausea and struggled to consume necessary energy gels, later stating, “After that half marathon, I was so sick.” In hindsight, she regrets not beginning with a lower 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. It was the first time she had raced on a GLP-1. She had taken her first 2.5mg standard starting dose of tirzepatide, commonly sold under the names Mounjaro and Zepbound, for weight loss, less than a week beforehand. 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. Reds is treated through adequate nutrition and exercise adjustments.
Data indicates that GLP-1 popularity is surging, with the proportion of people using these drugs for weight loss rising from 3% to 11% over the last two years. A 2026 cohort study reveals that non-FDA-approved usage has increased 15-fold compared to five years ago, with 35% of users falling outside the clinical definition of overweight by BMI standards. Meghann Featherstun, an Ohio-based sports dietitian, notes that these prescriptions have become significantly more accessible, requiring fewer clinical hurdles than in the past, leading to a growing client base among long-distance runners. The study also found that 35% of users are not considered overweight according to the BMI chart. 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. He went for casual runs, boxed and lifted weights, even when he wasn’t training for a long-distance race.
Perspectives among experts remain divided. Heidi Skolnik, a fellow of the American College of Sports Medicine, suggests that performance on GLP-1s is contingent upon an athlete’s ability to maintain hydration and caloric intake. “If you can eat enough to fuel your workouts and your runs and drink enough, then go for it. Good for you. But if you can’t, then don’t. Then you’re working against your health and wellbeing,” she stated. Conversely, researchers like Emily Lundstrom argue that athletes prioritizing performance should delay medication until their competitive cycle concludes. 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 toll can be substantial, with many users reporting gastrointestinal distress and reduced appetite. Steve, a 44-year-old from Oregon, began a tirzepatide compound in July 2026 to manage weight gain that persisted despite diligent macro tracking. During his initial training for an October half marathon, his resting heart rate spiked and his endurance plummeted. Only after halving his 2.5mg dose, a strategy he discovered online, did his training sessions stabilize. While Dr. Melanie Jay of the NYU Grossman School of Medicine confirms that GLP-1s can elevate resting heart rate by two to 10 beats per minute, she notes that individual responses to exercise vary. But now required multiple breaks and spiked his heart rate higher than usual, five miles usually came easy. A tip he saw on Reddit, steve cut his 2.5mg dose in half after four weeks.
Sports dietitian Claire Shorenstein strongly advises against using these drugs while actively training for endurance events. She warns that suppressing appetite while training leads to chronic low energy availability, which can trigger Relative Energy Deficiency in Sport (RED-S). This syndrome can diminish bone density, impair immunity, and in women, cause hypothalamic amenorrhea. Keri M confirmed experiencing these risks firsthand, noting that her underfueling during training for the 2026 Chicago race necessitated cycling her medication off and on. According to because marathoners and other endurance athletes are already at risk for underfueling, Shorenstein, Taking a GLP-1, which suppresses appetite, can lead to a chronic state of low energy availability, where the body doesn’t have enough energy left for “all the other functions that our body needs so that we can stay alive and be healthy”.
Other runners have faced similar dilemmas.
Kylie Keeton, a 32-year-old in Texas, turned to GLP-1s after noticing weight gain despite high mileage, only to find the nausea so debilitating she was forced to withdraw from a half marathon.
Despite trying various timing strategies—such as Kristy Baumann’s suggestion of dosing after long runs—Keeton eventually discontinued the drug.
Having lost only five pounds in six months, she concluded the side effects were not worth the expense.
Today, she trains without nausea and focuses on improving her performance metrics naturally. As the community continues to debate the role of these drugs in sports, experts emphasize that research into long-distance running specifically remains limited, necessitating extreme caution for anyone considering a combined approach.
