Period Changes on Ozempic, Wegovy, Mounjaro or Zepbound: What's Known and What the Labels Say

If your period has changed since you started semaglutide (Ozempic, Wegovy) or tirzepatide (Mounjaro, Zepbound), you’re not alone in noticing. The FDA labels don’t list menstrual disorders as side effects, and the big trials didn’t track cycles. What is well documented is that weight affects periods: losing weight can bring back ovulation in people whose cycles were irregular, and losing a lot of weight fast can delay a period. Here’s what the labels say, what tirzepatide means for the pill, what they say about pregnancy, how PCOS fits in and when to see a doctor.

What the labels say about periods

I searched the adverse reaction sections (section 6, including postmarketing reports) of the US labels for Wegovy, Ozempic, Mounjaro and Zepbound for “menstrual”, “amenorrhea”, “uterine”, “vaginal bleeding” and similar terms.

Labels checked on September 24, 2026.

The only cycle-related findings come from animal studies. In female rats, semaglutide lengthened the estrous cycle and slightly reduced the number of corpora lutea; the Wegovy label calls this likely an adaptive response to the drug’s effect on food intake and body weight. The estrous cycle is the rodent version of the menstrual cycle, and corpora lutea are what each ovulation leaves behind. With tirzepatide, more female rats had a prolonged phase of the cycle and fewer corpora lutea, effects the Zepbound label considers secondary to the drug’s effects on food consumption and body weight. These are animal data, but they point the same way as the rest of this article: eating less and losing weight affect ovulation.

The trials didn’t measure cycles. In STEP 1 (semaglutide 2.4 mg), 1,453 of 1,961 participants were women; in SURMOUNT-1 (tirzepatide), 1,714 of 2,539. Neither registered the menstrual cycle as an outcome. In the posted results, reproductive problems show up only as isolated serious events, and none reached 5% of any group, the cutoff for reporting non-serious events.

Why losing weight can change your period

Excess weight can disrupt ovulation. According to the 2025 position statement from the European Association for the Study of Obesity (EASO), women with obesity often have irregular periods and cycles without ovulation: fat tissue releases substances that interfere with how eggs mature. EASO cites evidence that losing 5% to 10% of body weight over 6 months helps restore ovulation and pregnancy in 55% to 100% of women. Weight loss on a GLP-1 is usually larger, as I explain in how much weight people lose on GLP-1 drugs. So it’s plausible that irregular cycles become more regular as weight comes off, though no large GLP-1 trial has measured it.

Losing a lot of weight fast can delay it. MedlinePlus defines secondary amenorrhea as going 6 months or more without a period after having normal cycles. It’s more likely with sudden large weight loss (strict diets, gastric bypass), low body fat (under 15% to 17%), excessive exercise, severe emotional distress, and also with obesity. The most common cause, it notes, is pregnancy.

If you’re eating very little because your appetite won’t allow more, tell your doctor; it affects vitamins and minerals too, as I cover in vitamins and minerals when you eat very little. If you’re skipping meals on purpose or you’re afraid of regaining weight, ask your doctor or a mental health professional for help.

The scale moves with your cycle, too. According to MedlinePlus, premenstrual symptoms start in the second half of the cycle and usually go away 1 to 2 days after your period starts. They include bloating and food cravings, and fluid retention can push weight up. More on that in weight-loss plateaus on GLP-1s and sweet cravings on Ozempic or Mounjaro.

GLP-1 drugs and polycystic ovary syndrome (PCOS)

The NHS lists PCOS, which it now calls polyendocrine metabolic ovarian syndrome (PMOS), among the common causes of missed or late periods. The 2023 international guideline defines an irregular cycle as shorter than 21 days or longer than 35, or fewer than 8 periods a year, from 3 years after the first period until perimenopause. On GLP-1 drugs, the guideline:

• Says liraglutide and semaglutide could be considered, alongside lifestyle changes, for higher weight in adults with PCOS, as in the general population.
• Recommends using them for ovulation or pregnancy outcomes only in research settings.
• Asks clinicians to ensure effective contraception during treatment when pregnancy is possible, because pregnancy safety data are lacking.

The studies show promise, but the evidence is weak. A 2023 meta-analysis of 11 trials with 840 women with PCOS found 72% more natural pregnancies and more regular periods with a GLP-1, though results on regularity varied enormously between studies. A 2026 meta-analysis, with authors from Sweden’s health technology assessment agency, pooled 11 trials: it found a modest drop in body mass index (1.38 points, low certainty) and not enough evidence to say whether periods become more regular. If you have PCOS, talk it through with your gynecologist or endocrinologist.

Tirzepatide and the pill

This is where the labels matter most, so here they are word for word.

Prescribing information (Zepbound; Mounjaro says the same): “Advise patients using oral hormonal contraceptives to switch to a non-oral contraceptive method, or add a barrier method of contraception for 4 weeks after initiation with ZEPBOUND and for 4 weeks after each dose escalation.” The label explains that tirzepatide delays stomach emptying, that this delay is largest after the first dose and diminishes over time, and that hormonal contraceptives not taken by mouth should not be affected.

Medication Guide (what patients get): “Birth control pills by mouth may not work as well while using ZEPBOUND. If you take birth control pills by mouth, your healthcare provider may recommend another type of birth control for 4 weeks after you start ZEPBOUND and for 4 weeks after each increase in your dose of ZEPBOUND.”

Europe sees it differently. The EU label for Mounjaro reports that after a single 5 mg dose, ethinyl estradiol peak levels fell 59% and total exposure 20%, but it doesn’t consider this clinically relevant and says no dose adjustment of oral contraceptives is required. The UK regulator, the MHRA, sides with the US advice: add a barrier method such as a condom for 4 weeks after starting Mounjaro and after each dose increase, or switch to a non-oral method.

Semaglutide. The US Wegovy and Ozempic labels carry no such advice, and the EU Wegovy label says semaglutide is not expected to reduce the effectiveness of oral contraceptives.

Which method suits you is a decision for you and your doctor, gynecologist or pharmacist.

Fertility, pregnancy and “Ozempic babies”

“Ozempic babies” is a phrase from social media and the press for unexpected pregnancies during treatment. I haven’t found regulator data on how many there are. A 2025 review in the American Journal of Obstetrics & Gynecology notes that many women with infrequent periods who had been unable to conceive have had unplanned pregnancies after losing weight on these drugs, but gives no numbers. Two explanations have a basis: weight loss can restore ovulation, and, with tirzepatide, the pill may work less well according to the US labels, although the EU label doesn’t consider that interaction relevant.

What the labels say about pregnancy:

• Wegovy. “Because of the potential for fetal harm, discontinue WEGOVY in patients at least 2 months before they plan to become pregnant to account for the long half-life of semaglutide.” For weight reduction, it also says to discontinue when a pregnancy is recognized.
• Ozempic. “Discontinue OZEMPIC in women at least 2 months before a planned pregnancy due to the long washout period for semaglutide.”
• Zepbound. Weight loss “offers no benefit to a pregnant patient and may cause fetal harm”; the label says to discontinue Zepbound when a pregnancy is recognized, and sets no stopping period before a planned pregnancy. The European Mounjaro label says to stop tirzepatide at least 1 month before a planned pregnancy.
• European labels. The EU labels for Wegovy, Ozempic and Mounjaro recommend that women who could become pregnant use contraception during treatment, and the Wegovy and Ozempic ones say to stop semaglutide at least 2 months before a planned pregnancy.
• Mounjaro (type 2 diabetes). The Medication Guide says: “Tell your healthcare provider if you become pregnant while using MOUNJARO.”

What if you get pregnant while taking one? Human data are still sparse. A 2026 systematic review of 36 studies concluded that, in large observational studies, exposure around conception or in early pregnancy wasn’t consistently linked to more major birth defects, compared with pregnant women on insulin or with the same condition. It’s a narrative synthesis without pooled data, and data on continued use through pregnancy are limited. The 2025 review is more cautious: with current evidence, effects on the baby can’t be predicted or ruled out. Wegovy and Zepbound both have pregnancy exposure registries, which your doctor can tell you about. Tell your doctor as soon as possible, and also if you’re planning a pregnancy.

Perimenopause: two changes at once

In STEP 1 and SURMOUNT-1 the average age was around 45, and perimenopause usually starts between 45 and 55, according to the NHS. One of its first signs, the NHS explains on its symptoms page, is periods that come more or less often and get heavier or lighter. Hot flashes, sleep problems and weight gain around the middle are common too. You can still get pregnant during perimenopause.

The NHS says to see a doctor if you’re bleeding more than before, not less, or if you have any bleeding after 12 months without a period. With two changes happening at once, it’s hard to tell what’s causing what, so let your doctor sort it out.

Heavier periods and iron

The NHS says your periods may be heavy if you need to change your pad or tampon every 1 to 2 hours, they last more than 7 days, you pass clots larger than about 2.5 cm (1 inch), you bleed through to clothes or bedding, or you often feel tired or short of breath.

According to MedlinePlus, heavy, long or frequent periods cause iron loss. Iron deficiency anemia starts with feeling weak or tired, headaches or dizziness, and later can bring pale skin, shortness of breath or hair loss. If you’re also eating less, less iron comes in with food. The NHS says your doctor may order blood tests to check for iron deficiency anemia. Which foods provide iron, what tests your doctor might order and when a supplement makes sense are in vitamins and minerals when you eat very little.

When to see a doctor

Make an appointment with your doctor or gynecologist if:

• Your period is late and you could be pregnant. Take a pregnancy test.
• You’ve missed 3 periods in a row or they’ve become irregular, according to the NHS. MedlinePlus is more cautious: see a provider if you’ve missed more than one.
• You’ve missed a period and have other symptoms, such as weight changes, tiredness, facial hair or dry or oily skin. The NHS notes thyroid problems or diabetes can also stop periods.
• You bleed heavily, between periods or after sex, or have severe period pain.
• You bleed after 12 months without a period.

Keep a note of your last few period dates; the notes field in the symptom diary works, and the doctor visit checklist helps you prepare questions. And always mention that you take a GLP-1, as I explain in telling people you take Ozempic.

Frequently asked questions

Is it normal to have heavier periods on Mounjaro or Zepbound?

The labels don’t list period changes as a side effect, and the trials didn’t measure them. Other causes, such as perimenopause or conditions of the uterus, are possible. If your periods are heavy or you feel tired or short of breath, see your doctor, who can check for anemia.

My period is late since I started Ozempic. Is that normal?

First rule out pregnancy with a test. Losing a lot of weight quickly can also delay a period, and so can stress, perimenopause or thyroid problems. If you’ve missed 3 in a row, or more than one according to MedlinePlus, make an appointment.

Does Zepbound make birth control pills less effective?

The US labels say tirzepatide may make the pill less effective and advise a non-oral or barrier method for 4 weeks after starting and after each dose increase. The European label doesn’t consider the interaction relevant, and the UK regulator advises adding a barrier method or switching to a non-oral one. Talk to your doctor or pharmacist before changing anything.

Can Ozempic be used for PCOS?

Not as an approved use: the US Ozempic label covers type 2 diabetes and lowering heart and kidney risks in some adults with it, and neither the US labels for Wegovy, Mounjaro and Zepbound nor the EU labels list PCOS among their indications^{[1,2,3,4,5,6,7]}. Using it for PCOS is off-label, a decision for your prescriber. The main hoped-for benefit is weight loss, which can bring back ovulation, as covered in why losing weight can change your period. But a 2026 meta-analysis of 11 trials found only a modest drop in BMI and not enough evidence on glucose, insulin, excess hair or cycle regularity^[11]. The guideline and both meta-analyses are in the PCOS section; typical weight loss is in how much weight people lose on GLP-1 drugs, and birth control and pregnancy in fertility and pregnancy. Talk it through with your gynecologist or endocrinologist.

I have PCOS and my period came back on Wegovy. Can I get pregnant?

Yes, it’s possible: weight loss can restore ovulation. The Wegovy label says to stop at least 2 months before a planned pregnancy. If you’re planning a pregnancy or think you might be pregnant, tell your doctor as soon as possible.

GLP-1 medications and menopause: does anything change?

The US labels for Ozempic, Wegovy, Mounjaro and Zepbound say nothing specific about menopause, and neither do the EU labels^{[1,2,3,4,5,6,7]}. A later Lilly-funded analysis of SURMOUNT-1 estimated reproductive stage, mostly from age, since the trial didn’t routinely record it: over 72 weeks on 15 mg of tirzepatide, women lost 26% of their weight before menopause and 23% during and after it, versus 2% to 3% on placebo^[23]. I haven’t found a similar analysis for semaglutide, where the data are mostly observational^[24]. A 2026 position statement from the Spanish Menopause Society asks clinicians to watch muscle and bone, with strength training and enough protein^[24]. The US Wegovy label reports more hip and pelvis fractures on Wegovy than on placebo in women in its cardiovascular outcomes trial: 1% vs. 0.2%^[3]. SYNCHRONIZE-HERA, a phase 3 trial of survodutide in women at this stage, isn’t recruiting yet^[25]. What’s known about GLP-1 medications at this stage is gathered in GLP-1 medications and menopause. Ask your doctor what this means for you.

Why do I gain weight before my period on Zepbound?

Fluid retention is common in the second half of the cycle, and the scale shows it even if you haven’t gained fat. According to MedlinePlus, these symptoms usually go away 1 to 2 days after your period starts.