New Research Is Looking at GLP-1 Drugs and Menstrual Side Effects

A woman starts taking a GLP-1 medication. A few weeks later, her period arrives unexpectedly. The bleeding is heavier than usual, or her menstrual cycle changes.

Did the medication cause it?

Until recently, researchers had relatively little systematic information to help answer that question.

Now, a study published in Obstetrics & Gynecology has identified menstrual adverse-event reporting signals associated with several widely used metabolic medicines.

The researchers examined reports involving female patients aged 12 to 55 and found that semaglutide, the active ingredient in Ozempic and Wegovy, had the broadest range of menstrual reporting signals.

Tirzepatide, the active ingredient in Mounjaro and Zepbound, showed a more limited pattern.

Liraglutide produced no statistically significant menstrual signals in the analysis.

The findings are important because GLP-1-based medicines are increasingly used by people of reproductive age, yet menstrual health has received relatively limited attention in their clinical safety literature.

But there is a critical distinction.

The study identified unusual patterns in adverse-event reports. It did not establish that these medicines cause menstrual disorders or determine how frequently such problems occur.

The research raises a question that deserves further investigation, rather than delivering a definitive answer.

Researchers have identified potential menstrual safety signals associated with semaglutide and tirzepatide.

A July 2026 pharmacovigilance study found disproportionate reporting of several menstrual events involving semaglutide, including heavy menstrual bleeding, bleeding between periods, menstrual clots, infrequent menstruation and anovulatory cycles.

Tirzepatide showed signals involving bleeding between periods and menstrual clots.

However, these findings came from a spontaneous adverse-event reporting database, not a clinical trial designed to measure menstrual changes.

The study cannot establish that the medicines caused the reported events.

Other factors, including weight changes, underlying reproductive conditions, pregnancy, hormonal contraception and metabolic health, may contribute to menstrual changes.

The practical takeaway is that menstrual health deserves attention during GLP-1 treatment, but an unexpected period should not automatically be attributed to the medication.

The research, titled Association of Glucagon-Like Peptide-1 Receptor Agonists With Menstrual Events in Reproductive-Aged Patients, was published online on July 9, 2026.

It was conducted by Connor Frey and Mahyar Etminan, researchers affiliated with the University of British Columbia and Epilytics.

The investigators analysed information from the US Food and Drug Administration's Adverse Event Reporting System, commonly known as FAERS.

The database collects suspected medication-related adverse events submitted by healthcare professionals, patients, manufacturers and other reporters.

The researchers examined reports available through March 2026.

They restricted their analysis to female patients aged 12 to 55 to focus on the population most relevant to menstrual outcomes.

The analysis included reports associated with three medicines:

The investigators searched for menstrual adverse-event patterns using two statistical approaches: disproportionality analysis and Bayesian analysis.

These techniques are commonly used in pharmacovigilance to identify potential safety concerns that warrant further investigation.

The study did not involve assigning patients to treatments, measuring menstrual cycles prospectively or comparing laboratory-confirmed hormonal changes.

Its results describe reporting patterns within a safety-surveillance database.

Source: Frey and Etminan, *Obstetrics & Gynecology*, July 2026.

The most notable finding concerned semaglutide.

Researchers identified disproportionate reporting across several menstrual outcomes.

These included heavy menstrual bleeding, intermenstrual bleeding, menstrual clots, oligomenorrhea and anovulatory cycles.

Some of these terms may be unfamiliar, but they describe different aspects of menstrual health.

Intermenstrual bleeding refers to bleeding between expected periods.

Oligomenorrhea refers to infrequent menstrual periods.

Anovulatory cycles are menstrual cycles in which ovulation does not occur.

These are not interchangeable conditions, and they can have different underlying causes.

The semaglutide findings in numbers

Source: Research findings reported by Contemporary OB/GYN, July 20, 2026.

The menstrual-clot result is particularly striking.

A reporting odds ratio of 31.63 is a substantial statistical signal.

However, it does not mean semaglutide makes someone 31 times more likely to experience menstrual clots.

A reporting odds ratio compares the relative frequency with which an event appears in reports involving a particular medicine against a reference group of other reports.

It is not a direct measure of disease risk.

It also does not tell us how many people taking semaglutide actually experience menstrual clots.

Some of the study's estimates were based on relatively small numbers of reports, making them less stable.

The investigators used Bayesian methods alongside conventional disproportionality analysis to assess the findings, but statistical consistency does not eliminate reporting bias or establish causation.

The important result is that semaglutide generated several signals that merit more focused reproductive-health research.

Tirzepatide did not produce the same broad range of menstrual signals in the study.

Instead, researchers identified two significant findings.

Intermenstrual bleeding had a reporting odds ratio of 1.64.

Menstrual clots had a reporting odds ratio of 5.41.

These signals indicate that the events were reported disproportionately within the study's statistical framework.

They do not establish that tirzepatide causes either condition.

They also do not demonstrate that tirzepatide is clinically safer than semaglutide for menstrual health.

The two medicines have different mechanisms of action and were introduced into the market at different times.

They are also used by populations that may differ in underlying conditions, treatment histories and reporting behaviour.

Semaglutide is a GLP-1 receptor agonist.

Tirzepatide activates both GIP and GLP-1 receptors.

Whether those pharmacological differences produce meaningful differences in menstrual outcomes remains uncertain.

A direct clinical comparison would require an appropriately designed study with clearly defined menstrual endpoints.

The current analysis cannot provide that answer.

The researchers also examined liraglutide, an established GLP-1 receptor agonist marketed in products including Victoza and Saxenda.

Unlike semaglutide and tirzepatide, liraglutide produced no statistically significant menstrual signals in this age-restricted analysis.

That finding should not be interpreted as proof that liraglutide cannot influence menstrual health.

The absence of a statistically significant signal can reflect several factors, including the number of reports available and differences between the populations being analysed.

Spontaneous-reporting databases are not designed to establish that one medicine has no risk simply because a particular signal is absent.

The study therefore identified different reporting patterns across the three medicines, not a definitive ranking of their reproductive safety.

This distinction is central to understanding the study.

Pharmacovigilance is the process of detecting, assessing and investigating possible adverse effects associated with medicines.

It is particularly important after a medicine becomes widely used.

Clinical trials can identify many adverse effects, but they may not be large enough or long enough to identify every uncommon event.

They may also collect certain outcomes more systematically than others.

For example, a weight-management trial may carefully measure changes in body weight, blood glucose, gastrointestinal symptoms and treatment discontinuation.

Menstrual-cycle changes may not be assessed with the same level of detail.

Spontaneous adverse-event reports can help identify potential problems that deserve additional investigation.

However, the FDA explicitly warns that the existence of an adverse-event report does not establish that the suspected medicine caused the event.

What the FDA says about reporting databases

The FDA identifies several important limitations:

• Reports may be incomplete or duplicated.
• The suspected medicine may not have caused the event.
• Underlying diseases or other treatments may explain some events.
• Reporting can increase when a particular issue receives publicity.
• The total number of people exposed to a medicine is generally unknown.

Consequently, these databases cannot establish the true incidence of an adverse event.

They also cannot reliably establish comparative safety between medicines on their own.

Source: FDA Adverse Event Monitoring System and database limitations.

This explains why the new menstrual findings deserve attention without being treated as confirmed medication side effects.

Possibly, and this is one of the most important unanswered questions.

Menstrual function is closely connected to metabolic health, energy availability and hormonal regulation.

Changes in body weight and nutritional status can influence the reproductive system.

Rapid weight loss or inadequate energy availability may disrupt the hormonal signals involved in ovulation and menstruation.

Conversely, improvements in metabolic health may help restore more regular cycles in some people who previously experienced reproductive dysfunction.

This creates an important problem when studying GLP-1 medicines.

If someone experiences menstrual changes while taking semaglutide, several explanations may be possible.

The medicine could potentially have a direct biological effect.

Weight loss or changes in energy balance could contribute.

An underlying condition could also explain the change.

The pharmacovigilance study cannot reliably distinguish among these possibilities.

Polycystic ovary syndrome complicates the picture

Polycystic ovary syndrome, or PCOS, is a common reproductive and metabolic condition associated with irregular ovulation and menstrual disturbances.

It is also frequently associated with insulin resistance and, in some patients, excess weight.

GLP-1 medicines have been investigated in people with PCOS because of their metabolic effects.

A systematic review and meta-analysis published in 2026 examined seven randomised controlled trials involving 330 women with PCOS.

The analysis found that liraglutide was associated with improvements in menstrual frequency, body mass index and insulin resistance compared with control treatments.

These findings suggest that metabolic treatment can be associated with improvements in reproductive outcomes in a specific patient population.

However, they do not establish that every GLP-1 medicine improves menstrual health.

They also do not rule out the possibility of adverse menstrual changes in other patients.

The review focused on women with PCOS, not the broader population of reproductive-aged GLP-1 users.

Source: Efficacy of liraglutide on metabolic and reproductive outcomes in women with PCOS, 2026.

The possibility of both beneficial and adverse menstrual changes is one reason the new research needs careful interpretation.

The July 2026 study raises this possibility but does not establish it.

The researchers proposed several potential mechanisms involving reproductive physiology.

These included possible activity involving GLP-1 receptors in endometrial tissue, changes in oestrogen metabolism associated with weight loss and downstream effects on coagulation pathways.

The endometrium is the tissue lining the uterus.

It undergoes hormonal changes throughout the menstrual cycle and is shed during menstruation when pregnancy does not occur.

Changes affecting endometrial function could theoretically influence bleeding patterns.

However, the study did not directly measure endometrial activity, reproductive hormone concentrations or coagulation changes in patients.

Its proposed mechanisms remain hypotheses.

The researchers did not demonstrate that semaglutide directly causes heavy menstrual bleeding through endometrial GLP-1 receptors.

Nor did they demonstrate that tirzepatide directly causes menstrual clot formation.

Those questions require experimental and clinical investigation.

The distinction between a possible mechanism and an established effect is particularly important when discussing reproductive health.

The July study is not the only recent research examining reproductive adverse-event reports.

A separate pharmacovigilance analysis published in Diabetes/Metabolism Research and Reviews examined FDA adverse-event data from the second quarter of 2022 through the second quarter of 2025.

The researchers investigated six GLP-1-based medicines, including semaglutide and tirzepatide.

The study identified 759 reproductive or endocrine-related cases and 1,276 alopecia-related cases.

It found elevated reporting odds for several reproductive and hormonal outcomes involving semaglutide.

However, tirzepatide showed lower reporting odds for several menstrual outcomes in that dataset.

These included abnormal uterine bleeding, painful menstruation, intermenstrual bleeding, menstrual irregularity, amenorrhea and heavy menstrual bleeding.

The researchers cautioned that these findings represented reporting patterns rather than comparative biological effects.

Source: Not All GLP-1 Receptor Agonists Are Alike, 2026.

A further 2026 analysis in Cureus compared gynaecological haemorrhagic reports involving tirzepatide and semaglutide.

It examined 103,607 female-specific adverse-event reports.

Gynaecological haemorrhagic events appeared in 0.60% of tirzepatide reports and 0.62% of semaglutide reports.

The relative reporting odds did not show a statistically significant difference between the two medicines.

These figures are proportions of adverse-event reports, not the percentage of all treated patients experiencing bleeding.

Source: Comparative Gynecological Safety of Tirzepatide vs Semaglutide, 2026.

Why do the findings differ?

The studies used different reporting periods, comparison groups, statistical adjustments and definitions of reproductive adverse events.

One analysis specifically restricted its population to female patients aged 12 to 55.

Others used different selection criteria or examined broader gynaecological outcomes.

These methodological differences can change which statistical signals appear.

The apparent disagreement does not establish that one investigation is necessarily correct and another is wrong.

It demonstrates that current pharmacovigilance findings are sensitive to how the data are analysed.

The evidence is not yet strong enough to establish a reliable ranking of menstrual risks among these medicines.

There is another reproductive-health issue that deserves attention when discussing GLP-1 medicines.

Some treatments can affect the absorption of oral medications because they slow gastric emptying.

This is particularly relevant to tirzepatide.

The FDA-approved prescribing information for Zepbound warns that tirzepatide may reduce the effectiveness of oral hormonal contraceptives.

The label advises people using oral hormonal contraception to switch to a non-oral method or add a barrier method for four weeks after starting treatment and for four weeks after each dose increase.

This recommendation is based on a recognised drug-interaction concern.

It is separate from the newly identified menstrual adverse-event signals.

What about semaglutide?

Semaglutide also slows gastric emptying, but its contraceptive interaction evidence is different.

A pharmacokinetic study involving 43 postmenopausal women with type 2 diabetes found that semaglutide did not reduce the overall exposure to the oral contraceptive components ethinylestradiol and levonorgestrel.

That finding does not mean every conceivable contraceptive interaction has been excluded.

It does mean that tirzepatide's specific oral-contraceptive warning should not automatically be applied to semaglutide as though the two medicines have identical interaction profiles.

Sources: Zepbound FDA prescribing information and semaglutide oral-contraceptive interaction study.

An unexpected menstrual change deserves attention, particularly if it is persistent, severe or substantially different from someone's usual pattern.

However, the timing of a symptom does not establish its cause.

Bleeding between periods, missed menstruation or unusually heavy bleeding can occur for reasons unrelated to GLP-1 treatment.

Potential explanations include pregnancy, hormonal contraception, PCOS, thyroid disorders, uterine fibroids, polyps and other reproductive conditions.

Weight changes and nutritional factors may also be relevant.

The American College of Obstetricians and Gynecologists (ACOG) identifies several patterns of abnormal uterine bleeding, including bleeding between periods, menstrual bleeding lasting longer than seven days and unusually heavy menstrual flow.

It also identifies the absence of menstruation for three to six months as a pattern requiring evaluation.

Source: ACOG, Abnormal Uterine Bleeding.

Information that can help a clinician assess the change

Relevant details include:

• When the menstrual change began.
• Whether the change occurred before or after GLP-1 treatment started.
• The usual menstrual-cycle pattern.
• The severity and duration of bleeding.
• Recent changes in body weight.
• Other medicines, including hormonal contraception.
• The possibility of pregnancy.
• Any associated pelvic pain, dizziness or unusual symptoms.

These details can help a healthcare professional consider possible causes.

They cannot independently establish that the GLP-1 medicine is responsible.

Patients should discuss suspected adverse effects with their prescribing clinician rather than making medication changes solely on the basis of a pharmacovigilance study.

Most menstrual irregularities are not medical emergencies.

However, severe bleeding or associated symptoms can indicate a more serious problem.

ACOG advises emergency medical care when someone is changing pads or tampons every hour for more than two consecutive hours and also experiences symptoms such as chest pain, shortness of breath, lightheadedness or dizziness.

Heavy bleeding accompanied by fainting or severe weakness also warrants urgent attention.

Severe pelvic or abdominal pain, particularly when pregnancy is possible, requires prompt medical assessment because conditions such as ectopic pregnancy can be dangerous.

A missed period followed by unusual bleeding should not automatically be interpreted as a medication side effect.

This is particularly important for people using tirzepatide alongside oral hormonal contraception because of the documented drug-interaction warning.

For a broader discussion of urgent medication reactions, see When a Peptide Side Effect Becomes a Medical Emergency.

The new study identifies several important questions but leaves fundamental gaps.

It cannot determine how many people taking semaglutide or tirzepatide experience menstrual changes.

It cannot establish whether the medicines directly cause those changes.

It cannot determine whether a particular menstrual event is more likely at one treatment stage than another.

Nor can it establish whether the effects are temporary, persistent or dependent on changes in body weight.

The research also cannot reliably separate the contribution of underlying conditions from the effects of medication.

What stronger research would look like

A prospective study could follow patients from before treatment begins and record menstrual outcomes systematically.

Researchers could document baseline cycle regularity, contraception, pregnancy status, underlying reproductive conditions and weight changes.

They could then measure outcomes such as bleeding duration, menstrual frequency, ovulation and relevant hormonal changes.

Appropriate comparison groups would help determine whether menstrual events occur more frequently among GLP-1 users than among otherwise similar people not receiving the medicines.

Such studies could also investigate whether menstrual changes resolve, persist or differ between individual medications.

Until this evidence becomes available, the current findings should be regarded as safety signals requiring investigation.

They are not established rates of drug-induced menstrual disorders.

Can semaglutide change your period?

A July 2026 pharmacovigilance study identified disproportionate reporting of several menstrual events involving semaglutide, including heavy bleeding, bleeding between periods and infrequent menstruation.

However, the study did not establish that semaglutide causes these changes or determine how often they occur.

Does Ozempic cause heavy menstrual bleeding?

Heavy menstrual bleeding generated a reporting signal for semaglutide, the active ingredient in Ozempic.

The study reported a reporting odds ratio of 3.51.

That does not mean Ozempic triples the risk of heavy bleeding. A controlled study is needed to determine whether a causal relationship exists.

Can Mounjaro cause irregular periods?

Tirzepatide, the active ingredient in Mounjaro, generated signals for bleeding between periods and menstrual clots in the July 2026 analysis.

A causal relationship has not been established.

Menstrual changes can also occur because of weight changes, underlying reproductive conditions and other factors.

Is tirzepatide safer than semaglutide for menstrual health?

The current evidence cannot establish that.

Different pharmacovigilance studies have produced different reporting patterns.

Without appropriately controlled comparative research, it is not possible to determine which medicine has a lower true risk of menstrual adverse effects.

Can GLP-1 drugs restore periods in women with PCOS?

Some clinical research suggests that certain GLP-1 medicines may improve menstrual frequency in women with PCOS.

A 2026 meta-analysis of seven randomised trials involving 330 women found improvements associated with liraglutide.

These findings apply to a specific patient population and do not establish that all GLP-1 medicines restore normal menstruation.

Can GLP-1 medications affect birth control?

Tirzepatide may reduce the effectiveness of oral hormonal contraception, according to its FDA prescribing information.

Semaglutide has different interaction evidence, including a study that did not find reduced exposure to two common oral contraceptive components.

Patients should discuss contraceptive considerations with their healthcare professional.

Should someone stop taking a GLP-1 drug if their period changes?

A menstrual change does not automatically establish that the medication caused it.

The FDA advises patients to consult their healthcare professional before changing or stopping prescribed treatment on the basis of adverse-event reporting data.

Severe bleeding or symptoms suggesting a medical emergency require immediate medical assessment.

Are menstrual side effects now officially established for all GLP-1 medicines?

No.

The July 2026 study identified pharmacovigilance signals, not confirmed causal adverse reactions across the entire drug class.

Additional research is needed to determine the true incidence, mechanisms and clinical significance of menstrual changes associated with individual GLP-1-based medicines.

The new research brings an overlooked question into focus.

GLP-1 medicines are widely used for diabetes and weight management, including by people of reproductive age. Yet menstrual outcomes have not been investigated as systematically as many other aspects of their safety.

The July 2026 study found disproportionate reporting of several menstrual events involving semaglutide.

Tirzepatide generated a narrower set of signals, while liraglutide produced no significant menstrual signals in the analysed population.

Those differences are worth investigating.

But spontaneous adverse-event reports cannot establish whether the medications caused the events, how commonly they occur or which treatment carries a lower true risk.

The reproductive-health picture is also more complicated than a simple list of adverse effects.

Weight loss and metabolic improvements may influence menstrual function, sometimes beneficially in people with conditions such as PCOS. Tirzepatide also has a documented interaction with oral hormonal contraception that requires separate consideration.

The important development is not that researchers have proved GLP-1 drugs cause menstrual disorders. It is that menstrual health is emerging as an area that deserves more systematic attention in the clinical evaluation of these medicines.

For patients experiencing unexpected changes, that means their concerns should be taken seriously without assuming the medication is necessarily responsible.

For researchers, it means the next step is clear: studies that measure menstrual outcomes directly rather than relying on spontaneous reports alone.

1. Frey C, Etminan M. (2026). Association of Glucagon-Like Peptide-1 Receptor Agonists With Menstrual Events in Reproductive-Aged Patients. Obstetrics & Gynecology. Published online July 9, 2026. DOI: 10.1097/AOG.0000000000006367. Read the original study on PubMed.

1. U.S. Food and Drug Administration. FDA Adverse Event Monitoring System Public Dashboard. Official explanation of spontaneous adverse-event reports, reporting bias, incomplete data and the limitations of estimating incidence or causality. Read the FDA information.

1. Not All GLP-1 Receptor Agonists Are Alike: Real-World Evidence of Differential Endocrine and Dermatologic Safety (2026). Diabetes/Metabolism Research and Reviews. A separate pharmacovigilance analysis identifying differing reproductive and endocrine reporting patterns among GLP-1-based medicines. Read the study on PubMed.

1. Efficacy of Liraglutide on Metabolic and Reproductive Outcomes in Women with Polycystic Ovary Syndrome (2026). Systematic review and meta-analysis of seven randomised controlled trials involving 330 women. Read the review on PubMed.

1. U.S. Food and Drug Administration. Zepbound (tirzepatide) Prescribing Information. Includes information about pregnancy and the interaction with oral hormonal contraceptives. Read the official prescribing information.

1. American College of Obstetricians and Gynecologists (ACOG). Abnormal Uterine Bleeding. Patient information explaining abnormal bleeding patterns, possible causes and symptoms requiring emergency medical attention. Read the ACOG guidance.

Medical Disclaimer

This article is for educational and research-information purposes only. It does not provide medical advice, diagnosis or treatment recommendations. Menstrual changes can have many causes, and current pharmacovigilance findings do not establish that GLP-1 medicines cause menstrual disorders. Consult a qualified healthcare professional about unexpected menstrual changes, contraception, pregnancy concerns or personal medication decisions. Seek urgent medical care for severe bleeding, fainting or other symptoms that may indicate a medical emergency.