This week: the side effect women keep talking about that still is not in the label, and the one that is in the label but may be blaming the wrong culprit.

Let's go. ☕

THE BIG ONE

Semaglutide (Wegovy, Ozempic) and tirzepatide (Zepbound, Mounjaro) are FDA-approved drug products. Menstrual-cycle changes are not currently listed as adverse reactions in the Wegovy or Zepbound prescribing information.

Your period changed. Here is what we actually know.

"Three periods in six weeks. Then nothing for two months. My doctor shrugged."

Women are describing timing changes, spotting, heavier or lighter bleeding, missed periods, and cycles that suddenly feel different after starting GLP-1 treatment. The experience may be real. The harder question is why.

Is it the medication? The weight loss? PCOS waking back up? A change in energy intake? Something completely unrelated? Right now, the evidence cannot cleanly separate those possibilities.

WEIGHT LOSS CAN MOVE THE REPRODUCTIVE SYSTEM IN EITHER DIRECTION

Your reproductive system pays attention to energy availability. Significant weight loss or a prolonged energy deficit can alter signaling through the hypothalamic-pituitary-ovarian axis and, in some people, contribute to delayed or absent periods.

But there is another side to the story. In women with obesity and previously irregular cycles, major weight loss can actually make periods more regular. Bariatric-surgery studies consistently show improved menstrual regularity and reproductive function after substantial weight loss.

So weight loss does not push every cycle in the same direction. Sometimes the cycle gets disrupted. Sometimes a previously disrupted cycle starts working better.

FOR PCOS, THE SYSTEM MAY START SWITCHING BACK ON

This is especially important for women with PCOS. GLP-1 treatments can improve weight and insulin resistance, and studies in women with PCOS have reported improvements in menstrual regularity and natural pregnancy rates.

A 2026 study of 96 women with chronic irregular cycles and anovulation found that after six months of semaglutide treatment, ovulatory cycles returned in about half of those who had previously been anovulatory.

That does not mean semaglutide is a fertility drug. It does mean one thing worth remembering: irregular periods do not guarantee absent ovulation forever. If cycles become more regular as metabolic health improves, pregnancy may become possible even when it was difficult before.

And both Wegovy and Zepbound prescribing information say treatment should be discontinued when pregnancy is recognized because weight loss offers no benefit during pregnancy and fetal risk is possible.

THE ONE REPRODUCTIVE WARNING THAT ACTUALLY IS IN THE LABEL

Tirzepatide has a very specific contraceptive warning. Zepbound delays stomach emptying, which can reduce the effectiveness of oral hormonal contraceptives. Its prescribing information advises people taking the pill to switch to a non-oral contraceptive method or add a barrier method for four weeks after starting Zepbound and four weeks after every dose increase.

Non-oral hormonal contraceptives are not expected to be affected in the same way. Wegovy does not carry an equivalent oral-contraceptive backup recommendation.

This is probably the most practical reproductive-health fact in either label. And it is not the one going viral.

WHAT WE STILL DO NOT KNOW

The pivotal weight-loss trials did not establish menstrual-cycle changes as an adverse effect, and neither Wegovy nor Zepbound currently lists menstrual irregularity in its adverse-reaction section. But the story does not stop there.

A July 2026 pharmacovigilance study looked at FDA Adverse Event Reporting System data through March 2026. Semaglutide showed disproportionate reporting signals for heavy menstrual bleeding, bleeding between periods, menstrual clots, oligomenorrhea, and anovulatory cycles. Tirzepatide showed signals for intermenstrual bleeding and menstrual clots.

Important distinction: a reporting signal is not proof that the drug caused the event. FAERS cannot tell us how common these problems are, and it cannot separate the medication from weight loss, PCOS, age, other medications, or underlying hormonal conditions. But it tells us the question is worth studying properly.

So when someone asks: is this the drug, the weight loss, or my hormones? The most accurate answer right now is: we do not know yet.

THE FEMALE DATA GAP

The label has an answer about the pill. It still does not have an answer for the woman asking why her period suddenly changed.

DEINFLUENCED

This one gets blamed directly on the drug. And unlike menstrual changes, hair loss is in the prescribing information.

WHAT THE EVIDENCE SAYS

The shedding is real. With Wegovy 2.4 mg, hair loss was reported in 3.3% of treated adults versus 1% with placebo. Among women specifically, the rates were 4% versus 2%. With Zepbound, hair loss occurred in roughly 4% to 5% of participants depending on dose versus 1% with placebo. Among women, it was reported in 7.1% with Zepbound versus 1.3% with placebo.

And here is an unusually helpful detail: both labels connect the hair-loss reports with weight reduction. That fits with a familiar dermatology phenomenon called telogen effluvium. A major physical stressor, sudden weight loss, illness, surgery, or nutritional change can push a larger-than-usual number of hair follicles into their resting phase.

Then comes the frustrating part: the shedding often does not start immediately. It commonly appears about two to four months after the trigger. So by the time your hair starts showing up everywhere, the event that triggered it may already be months behind you. If the trigger settles, acute telogen effluvium is usually self-limited, with hair loss often normalizing over roughly six to nine months.

Does that prove the medication molecule has nothing to do with it? No. But the leading explanation is the rapid weight loss, reduced intake, and physiological stress that can accompany treatment rather than a drug directly attacking the hair follicle. And because telogen effluvium runs on a delay, changing treatment today does not necessarily make shedding stop tomorrow.

If the hair loss is patchy, associated with scalp changes, unusually severe, or keeps going without improvement, that is a different conversation than a forum diagnosis.

ASK A CLINICIAN

This is one of those rare times when the prescribing information gives a very specific answer. Zepbound slows stomach emptying, and that can reduce how well an oral hormonal contraceptive is absorbed.

Because of that, the label advises people using the pill to either switch to a non-oral contraceptive method or add a barrier method for four weeks after starting Zepbound and for four weeks after every dose increase. That warning is specific to oral hormonal contraception. Non-oral hormonal methods are not expected to be affected in the same way.

So if you just started Zepbound or recently increased the dose and nobody discussed your birth control with you, I would bring it up with your pharmacist or prescriber now rather than waiting for your next routine appointment.

And there is one more reason this matters. For some women with PCOS, weight loss and improved metabolic health can make cycles more regular and ovulation more likely. So a history of irregular periods is not something I would use as reassurance that pregnancy cannot happen.

Mais, PharmD

Medical Reviewer, Pep in Her Step

ON THE RADAR

This issue was medically reviewed by Mais, PharmD.
Pep in Her Step is education, not medical advice.
Talk to your prescriber before doing anything peptide-shaped.
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