Study Reveals Unknown GLP-1 Side Effects Reported on Reddit

With any medication, the official label spells out the laundry list of risks pulled from clinical trials. But controlled studies don’t always reflect how a drug is experienced in the real world. When it comes to GLP-1 drugs like Ozempic, Wegovy, and Zepbound, there are growing anecdotal reports on social media of less-recognized symptoms, according to a recent study published in Nature Health. We interviewed the lead author of the study and doctors to find out whether these previously unknown side effects can affect performance and how to adjust your workouts when taking a GLP-1.

What GLP-1 Side Effects Did Redditors Report?

Using AI, the study researchers analyzed more than 400,000 Reddit posts written by people who mentioned GLP-1s. Upon reviewing those 400,000 posts, nearly 70,000 people reported taking a GLP-1 medication (semaglutide or tirzepatide); the posts analyzed were dated between May 2019 and June 2025. Alongside well-established side effects like nausea, fatigue, and constipation, researchers found that nearly four percent of Reddit users also described hot flashes, chills, fever, and menstrual changes like irregular or unusually heavy bleeding.

“We can’t say for certain whether these drugs are causing menstrual irregularities or temperature regulation issues,” Neil Seghal, lead author of the study, tells Outside. Rather, the social media reports suggest there may be other side effects that researchers should be looking at based on real-world use because the way people are using GLP-1s—microdosing them or using compounded formulations—diverges from how they’re used in clinical trials, he says.

Of course, anecdotal data (particularly from self-reported, anonymous forums like Reddit) comes with limitations. People may have other underlying health conditions or lifestyle factors that explain their symptoms independently of the medication itself. For instance, “a woman who is in perimenopause or menopause could experience hot flashes because of estrogen depletion,” Dr. Yuval Pinto, an obesity medicine physician at Johns Hopkins Medicine, tells Outside.

Still, there are a few biologically plausible explanations for why these patterns may show up. For one, rapid weight loss (whether from medication, diet, or other lifestyle habits) is known to temporarily disrupt hormonal levels. In regard to thermoregulation, which refers to the body’s ability to control its temperature, by losing body fat, “you’re losing insulation, so thereby it follows that you’re less tolerant to the cold,” says Dr. Nora Lansen, board-certified family physician and chief medical officer of Elektra Health, a women’s telemedicine service.

Those shifts aren’t just uncomfortable, though. For physically active users, they may subtly affect recovery, endurance, and performance over time.

How Can GLP-1 Body Temperature and Hormonal Changes Impact Your Workouts and Outdoor Adventures?

Even outside the context of GLP-1s, disruptions in temperature regulation and menstrual function can make exercise feel harder than usual. Take hot flashes—those spontaneous waves of warmth that typically flood the chest, neck, and face, and are followed by sweating. Beyond discomfort, they’re also commonly accompanied by fatigue, dizziness, and nausea, all of which can make it more difficult to sustain longer or higher-intensity efforts. Staying hot for too long during exercise can also cause fainting. This is especially relevant if you’re running or hiking in the outdoors on a hot day.

Existing research shows that menstrual changes (like heavier bleeding) can increase iron loss, which plays an important role in transporting oxygen and energy production. Over time, low iron levels can make someone feel more winded, less powerful, or generally “off” during workouts. If you’re feeling dizzy or less alert, this can make navigating the outdoors potentially dangerous. So, it’s crucial to listen to your body, whether you’re at the gym or on the trail.

Layer known GLP-1 side effects on top of body temp and menstrual/hormonal changes, and the effects on athletic performance compound. Remember, “many patients on a GLP-1 are under-eating and slightly dehydrated,” says Dr. Hector Perez, a bariatric surgeon and internal medicine physician at Montefiore Medical Group in Bronx, New York, tells Outside. Sometimes, how much a person drinks or eats while on a GLP-1 is dramatic, which impairs their temperature regulation, Perez says. Not consuming enough nutrients and water also leaves the body without sufficient fuel for training and recovery.

How to Adjust Your Training When Taking a GLP-1 (Without Quitting Altogether)

Here are some tricks to make training more accessible even when the body is going through changes associated with GLP-1s.

1. Pull Back on Intensity When Symptoms Flare

Resistance training remains one of the best ways to maintain muscle during weight loss, says Lansen. There’s even evidence to support that it may ease hormone-related symptoms like hot flashes, too.

However, high-intensity workouts can add stress to a body that’s already running on low energy, on top of adjusting to dizziness, fatigue, or extreme temperature swings. While you don’t have to skip movement altogether, it’s important to, at the very least, start with a gentle warmup, says Dr. Sarah Eby, a sports medicine physician at Mass General Brigham and assistant professor of physical medicine and rehabilitation at Harvard Medical School. “And extend it longer than you usually would if you’re experiencing chills from a medication.”

Instead of pushing through an unusually difficult HIIT workout, Eby suggests lower-intensity options like incline walking, cycling at a conversational pace, or strength training with higher reps and lower weights. She says yoga is a great option, too.

2. Be Strategic About Where and When You Exercise

If your internal thermostat feels off, your surroundings matter more than usual.

“Exercise in cooler temperatures, whether that’s earlier in the morning or indoors in an air-conditioned environment,” Eby recommends to anyone prone to overheating or hot flashes. “Also have cold water by your side and make sure to stay out of the sun.” And Pinto suggests working out near a fan if possible.

3. Hydrate Proactively, Not Reactively

GLP-1s can blunt appetite and thirst cues, making it easy to unintentionally under-hydrate.

A general baseline (eight to 12 cups of water each day) is a good starting point, though “adding sodium—either through food or a simple electrolyte mix—helps retain fluid and improves dizziness and chills,” Perez says. But because GLP-1s in particular also make you feel full quickly, “spacing fluids away from meals can help,” he adds. “Small, frequent sips throughout the day are often better tolerated than large volumes at once.”

4. Remember to Fuel—Even When You’re Not That Hungry

“Training fasted or under-fueled can worsen that shaky, flushed feeling,” Perez says, which is why a pre-workout snack goes a long way. Look for easy-to-tolerate combinations of carbs and protein—yogurt with fruit, half a banana with peanut butter, or a handful of nuts. It doesn’t have to be a full meal; it just has to give your body something to work with.

Usually, that drop in energy or that “why does this suddenly feel so hard?” moment is a frustrating yet common part of adjusting to a GLP-1, Pinto says. He encourages people to take it easy and give themselves time to adjust, whether that involves pulling back temporarily or redefining what a “good” workout looks like right now. “Any movement is a blessing,” he says, noting that the best, most fulfilling routine is the one you enjoy.

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