Laura Bradley
Mon, August 10, 2026 at 5:13 PM UTC
A new analysis of an FDA database found that GLP-1 medications were associated with menstrual changes
The research does not prove that these weight loss medications cause these effects
Experts say you don’t have to avoid GLP-1 medications based on these findings, but should recognize that menstrual changes may happen
Millions of people worldwide take obesity medications like Ozempic and Zepbound, which are well known for gastrointestinal side effects like nausea and bloating
But a recent analysis of the FDA’s adverse event reporting system suggests that the popular drugs, known as GLP-1s, may be linked to a less recognized effect: menstrual changes such as heavier periods and blood clots
The research, which was published in July in the journal Obstetrics & Gynecology, can’t prove that these medications cause concerning period changes. Still, the findings are helpful to be aware of, said Alyssa Dominguez, MD, a clinical assistant professor of medicine with the Keck School of Medicine of USC and endocrinologist with Keck Medicine, who wasn’t involved with the new study.
Analyzing Complaints By GLP-1 Users
The new study was inspired by an earlier analysis, which found that adverse menstrual changes accounted for nearly 4% of all side effects reported on Reddit forums by people taking semaglutide and tirzepatide
Those changes weren’t “systematically captured” in the clinical trials evaluating the medications MD, an internal medicine resident physician at the University of British Columbia and an author of the new study
“That patient-reported signal was well ahead of the peer-reviewed literature,” Frey told HEALTH. “We wanted to see if it held up in a formal pharmacovigilance database using statistical methods.”
To find out, the researchers turned to the FDA’s Adverse Event Reporting System (FAERS), a database that tracks problems with drugs after they enter the market.
They analyzed reports submitted through March 2026 involving female patients ages 12 to 55 taking the GLP-1 medications semaglutide, tirzepatide, or liraglutide. The team then compared the number of negative menstruation-related reports for each drug with the number that chance would predict based on reporting patterns for all other medications in the database
Menstrual Changes Reported at Higher Rates
Liraglutide showed no significant menstrual-related adverse events. However, people taking semaglutide and tirzepatide reported these changes at higher-than-expected rates
“Semaglutide had by far the broader and stronger signal profile,” Frey said.
Patients reported menstrual clots at 31.63 times the expected rate, while abnormal menstrual clots occurred at 10.75 times than would be expected. Other higher-than-expected reports included heavy menstrual bleeding, vaginal bleeding between periods, anovulatory cycles (when the ovaries do not produce an egg), infrequent periods, and menstrual disorders.
“Tirzepatide’s signal was narrower,” People reported menstrual clots at 5.41 times the expected rate and intermenstrual bleeding at 1.64 times more often
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There are some important caveats, though. Because the FDA’s adverse reporting database relies on voluntary reports, it’s unclear how many people were taking the drugs during the study period or how many experienced no menstrual changes—or even improvements. Popular drugs like GLP-1s, which receive heavy news coverage, also tend to generate more reports, potentially skewing the results
Based on the study design, the results are “not very generalizable,” Dominguez said
From what Dominguez has seen, GLP-1s may actually improve menstrual regularity for people with polyendocrine metabolic ovarian syndrome (PMOS, formerly known as PCOS). “Anecdotally, I can say that more people I’ve talked to have had improvements in their menstrual symptoms rather than worsening,” she said. “So, in some ways, this study actually surprised me.”
Still, Dominguez acknowledged that “there does seem to be a group that maybe will have a negative effect.”
Looking ahead, Frey believes studies that track menstrual cycles in real time could help researchers better understand the connection between GLP-1s and unwanted menstrual changes
What Could Be Behind the Connection?
Again, the study doesn’t prove that GLP-1s cause adverse menstrual changes. But if they are playing a role in these outcomes, why might that be happening?
It’s well established that weight loss can affect the menstrual cycle, but Frey doesn’t think that explains the findings in this case
Some of the outcomes from weight-related metabolic disruption—such as irregular menstruation, severe menstrual cramps, and shorter menstrual cycles—weren’t reported at higher-than-expected rates. Instead, Frey said, the complaints reported at disproportionately higher rates represented “a more specific cluster.”
According to Frey, that suggests that any potential effect on menstruation may be related to the drugs themselves rather than solely a secondary effect of weight loss
What the Findings Mean For You
Frey doesn’t believe people should avoid taking GLP-1 medications or undergo routine testing before starting them solely based on the results of his study. Rather, like Dominguez, he thinks the bigger takeaway is to simply recognize that menstrual changes may occur
If you’re taking a GLP-1, or even if you’re not, it’s important to tell your doctor if you notice changes to your menstrual cycle. They can help determine what might be causing them
“In the absence of a menstrual period, we would want to consider things like pregnancy or losing periods from too much weight loss,” Dominguez said. “Or, if periods are all of a sudden becoming very heavy or irregular, we would want to look more into why that is happening.”
Read the original article on Health
