400,000 Reddit Posts Point to These Potential GLP-1 Side Effects

17.09.2026, 02:17 allure.com

When you’re dealing with new period changes and bouts of fatigue that coincides with starting a GLP-1 medication, an eyebrow raise is only natural—especially when most chatter about the drugs’ side effects is focused on nausea and diarrhea (how glamorous!). But as the drug category becomes more widely-used, patients are reporting other symptoms that don’t make it on the label, and a new Nature Health study dives into them.

For the study, researchers conducted an AI analysis of 400,000 Reddit posts shared over more than five years to find an array of symptoms reported by people who use semaglutide (Ozempic, Wegovy, and Rybelsus) and tirzepatide (Mounjaro and Zepbound).

Researchers found posts from 67,008 users on well-known side effects like nausea, vomiting, constipation, and diarrhea. More interestingly, they also discovered symptoms that aren’t typically linked with GLP-1s. Some of the more commonly-reported yet surprising complications were fatigue, menstrual irregularities, chills, and hot flashes.

It’s worth noting that other studies have looked at the drugs’ effects on everything from nail-biting to hair loss, suggesting that the list of official side effects linked with these medications may grow with time. Separately, it seems increasing numbers of people are obtaining these medications through outside of their doctors office, which, as Allure has previously reported, can coincide with patients taking higher-than-recommended doses or following aggressive titration schedules that could increase the possibility of side effects that might not happen when the drugs are taken as directed. This gray market also makes it difficult for those patients to get the appropriate care they need if side effects do surface.

But back to the study: To be clear, it did not conclusively prove that GLP-1s caused these side effects—it just established a link—and some of them may be due to weight loss rather than the medications themselves. But the researchers wrote in the study that these findings are worth digging into deeper, noting that they “highlight patient concerns not well captured in current labelling or trials.”

While some of the symptoms flagged aren’t the ones everyone associates with these medications, health care providers who treat patients on GLP-1s say they’ve heard them all before.

Even with some of the more commonly associated side effects—like hair loss and skin changes—a lot of it is believed to be due to the rapid weight loss many patients experience when taking GLP-1 medication (up to 20% of their body weight over 72 weeks) rather than the drug itself.

But there are changes that happen in the body beyond fat loss while someone is on a weight loss journey, says Mir Ali, MD, medical director of MemorialCare Surgical Weight Loss Center at Orange Coast Medical Center in Fountain Valley, CA. “Many are tied to changes in hormones,” he says.

Studies have found that circulating levels of estrogen typically drop in women when they lose significant amounts of weight, Dr. Ali explains. In men, testosterone levels tend to increase with weight loss. These hormone changes could play a role in some of the surprising side effects flagged in the study, but not all of them.

Of the side effects highlighted in the new study, changes in menstrual cycles “make the most sense to me clinically,” says Kelley Gregorovic, MS, a board-certified family nurse practitioner at Tufts Medicine Weight and Wellness Center at Melrose Wakefield Hospital. “Recent analyses of FDA adverse event reports have found menstrual changes with some GLP-1 medications,” she says. These include heavier-than-usual bleeding, blood clots, and bleeding between periods. “That still doesn't prove the medication is causing them, but it tells us this is something worth paying attention to and studying further,” Gregorovic says.

In patients with certain preexisting conditions, weight loss can sometimes improve menstruation-related symptoms. "If someone has a history of PMOS or PCOS diagnosis, they can experience an improvement in period regularity as their obesity and insulin resistance improves," says Rutuja Patel, DO, medical director of medical weight management at Northwestern Medicine Central DuPage Hospital and Northwestern Medicine Delnor Hospital. On the flip side, “rapid weight loss or not eating enough can disrupt menstrual cycles,” Gregorovic says.

Perimenopause can also be a factor in what women notice when starting a GLP-1. “If a woman starts a GLP-1 in midlife and her periods change, we can't automatically assume it's the medication,” Gregorovic says. (A recent KFF survey found that GLP-1 use is highest in women between the ages of 50 and 64, but the second highest is in ages 30-49, which would include the years when most people start perimenopause.)

“Her weight may be changing, her metabolic health may be changing, and her hormones may be changing, all at the same time,” Gregorovic says. That makes it difficult to tell what’s actually driving the menstrual changes, she adds.

Fatigue is a common symptom flagged by GLP-1 users due to a change in eating habits and weight loss, according to Dr. Ali. “They’re going through a drastic change in diet and weight, and the body has to adjust to that,” he says. (This tends to improve as people hit a steady diet and exercise routine that keeps them at a weight they're comfortable with, he adds.)

“Fatigue, I absolutely see, and that's when I become a bit of a detective,” Gregorovic says. GLP-1s suppress appetite, which can be too effective in some patients. “If someone is exhausted, I start asking questions. ‘Are you eating enough? Getting enough protein? Hydrating? Are you losing weight too quickly? Are you losing muscle? How are you sleeping?’” she says. “If we've addressed those things and the fatigue is still there, then I want to look a little deeper.”

That may involve doing lab work to look for things like anemia, nutritional deficiencies, or thyroid dysfunction. “I don't want to just chalk fatigue up to the medication when there may be something else going on that we can identify and address,” Gregorovic says.

Gregorovic says she’s “more cautious” about linking hot flashes and chills directly to GLP-1 medications, and Dr. Ali agrees. “It’s not a common complaint I get,” he says.

Dr. Patel echoes that. “These side effects are not very common,” she says. But if someone is having hot flashes and chills, “the most important thing to determine is whether they are eating enough nutrients to keep up with their needs,” she says. Among other things, the loss of body fat means there’s less insulation to keep you warm, which could cause you to feel chilly more easily than before.

Despite what the new study found, gastrointestinal side effects are still the most common complaints the providers Allure spoke with for this story hear from patients who are taking GLP-1s. “The most common side effects are nausea, constipation, diarrhea, and/or vomiting when starting and when escalating doses,” Dr. Patel says. “We usually address these side effects by making specific changes to diet.”

While these can be uncomfortable and disruptive, they don’t last forever. “They tend to be short-lived and improve with time,” Dr. Ali says.

Another common side effect is appetite suppression that is more severe than people want. “Patients should talk to their doctor to check for nutrient deficiencies and make sure their weight loss is appropriate,” Dr. Patel says.

All of this is why Allure recommends working with a health care provider—not an AI chatbot on a telehealth company’s website—when you’re on a GLP-1 medication. If you’re having any of the aforementioned lesser known symptoms after starting a GLP-1 medication, tell your doctor. It’s easy to downplay a new symptom on a GLP-1 that seems unrelated. But health care providers say the latest findings are a good reminder that every shift matters.

If you notice a symptom that comes and goes, Dr. Ali says it’s likely no big deal or possibly unrelated to your new medication. “But if the side effects are significantly affecting you in any way or preventing you from normal day-to-day activities, you should talk to your provider,” he says. “Sometimes the dose can be adjusted or other things can be done.”

But if the symptoms are sticking around, especially after a dose change, don’t be shy about speaking up at your next appointment. For example, "If period irregularity doesn’t improve in one to two cycles, it’s important that the patient also talk to their gynecologist,” Dr. Patel says.Gregorovic emphasizes that this type of communication should go both ways. “When patients repeatedly tell us, ‘Something changed when I started this medication,’ I think we should listen,” Gregorovic agrees. “That doesn't mean the medication caused it, but it does give us something worth looking into.”

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