A new study published in the journal Nature suggests that widely used weight-loss drugs may be tied to side effects not fully captured in clinical trials.
Researchers at the University of Pennsylvania analyzed more than 400,000 Reddit posts from over 67,000 users taking GLP-1 medications. These drugs include semaglutide, sold as Ozempic and Wegovy, and tirzepatide, sold as Mounjaro and Zepbound.
GLP-1 drugs are commonly prescribed for diabetes and weight loss. The Mayo Clinic has linked them to known side effects such as nausea, vomiting, diarrhea, and constipation.
The new analysis confirmed those common issues. About 44 percent of users reported at least one side effect. Around 37 percent said they experienced nausea. Researchers said the data suggests the method is picking up real signals from patients.
But researchers also found less commonly discussed symptoms.
About 4 percent of users reported menstrual irregularities. These included heavy bleeding, irregular cycles, and other reproductive changes. Some users also described temperature-related symptoms such as chills, hot flashes, and fever-like feelings.
Researchers said the findings may highlight gaps in traditional clinical trials.
“People often use medications differently than they’re prescribed,” lead researcher Neil Sehgal told Fox News Digital. “So there are many possible reasons we’re seeing signals that the trials may have missed.”
Mental health symptoms also appeared in the data. Nearly 13 percent of users reported anxiety, depression, or insomnia. Others mentioned fatigue, dizziness, headaches, and acid reflux.
Fatigue stood out in particular. Researchers said it was one of the most common complaints. It has not been widely reported in clinical trials.
Doctors say some of these symptoms may have simpler explanations.
Dr. Sue Decotiis, a weight-loss physician in New York City, said issues like fatigue and disorientation may be linked to dehydration or low blood sugar. She said patients should be closely monitored and stay properly hydrated while using these medications.
She also warned that some people are using these drugs without proper medical guidance. That can raise the risk of complications.
Researchers stressed that the study has limits.
The data came from Reddit users, who tend to be younger and mostly male. That group may not represent the broader population. People who have negative experiences may also be more likely to post online.
The study also cannot prove that the drugs caused the symptoms.
“We can’t say that GLP-1s are actually causing these symptoms,” Sehgal said.
He added that the findings should be seen as early signals, not final conclusions. More research is needed to confirm any link.
For now, experts say patients should speak with their doctor if they notice unusual symptoms while taking these medications.