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What is Mounjaro (Tirzepatide)?
Mounjaro (tirzepatide) is a prescription medication commonly prescribed to support weight loss in those who are overweight or living with obesity. It works by targeting two natural hormones in the body called GLP-1 (glucagon-like peptide-1) and GIP (glucose-dependent insulinotropic polypeptide)(1). These hormones help control blood sugar levels, cholesterol, appetite, feelings of fullness and how the body uses insulin(1). Because of these effects, Mounjaro can help people feel full sooner, eat less, and lose weight while also improving blood sugar control. As your body adjusts to the medication and weight changes, you may notice some changes in other parts of your health, including your menstrual cycle.
Can rapid weight loss affect your period?
Rapid weight loss can affect your menstrual cycle, whether it happens with medication, dieting, or lifestyle changes. Your body needs a certain amount of energy and body fat to maintain normal hormone production. When weight drops quickly or calorie intake becomes very low, the brain may temporarily adjust reproductive hormone signals while your body adapts to the new weight3. This can lead to delayed or missed periods, irregular cycle timing, changes in bleeding amount and temporary changes in ovulation.
Does Mounjaro affect your menstrual cycle?
Some women report changes to their menstrual cycle while taking Mounjaro. Although this is not listed as a common side effect, Mounjaro can influence several factors that affect your period, including weight, hormone levels, blood sugar control and insulin sensitivity. Because the menstrual cycle is closely linked to hormones and body weight, these changes may lead to temporary differences in your cycle, such as irregular timing or changes in bleeding.
What effects may Mounjaro have on your period?
Hormonal changes
Some women taking Mounjaro report changes to their menstrual cycle. These can vary from person to person. Mounjaro improves the way the body responds to insulin, which is helpful for blood sugar control but as insulin also interacts with several other hormones involved in the menstrual cycle, these can be temporary changes.
By improving insulin sensitivity, Mounjaro may indirectly influence:
- Oestrogen (which has a key role in the following: reproductive system, bone/muscle health, cardiovascular health, brain/mood and skin/tissue).
- Progesterone (menstrual cycle regulation, pregnancy maintenance and balancing oestrogen)
These hormone shifts may slightly change the timing or pattern of your cycle while your body adjusts. Weight loss can also affect stress-related hormones such as cortisol, which can sometimes contribute to temporary menstrual changes, while helping to balance the cortisol and improve the body’s regulation of it.
Temporary menstrual cycle irregularities
Some women notice cycle irregularities after starting Mounjaro or during periods of rapid weight loss or reduce calorie intake. It can also be due to hormonal adjustments as insulin levels improve. Ovulation patterns may also temporarily shift, which can affect when your period arrives. For most women, cycles settle again once weight stabilises.
The possible cycle changes include2
- Change in duration of cycles
- More predictable cycles
- Spotting between periods
- Lighter or heavier bleeding – linked to hormonal fluctuations, changes in ovulation and oestrogen levels due to weight loss
- Skipped periods
If bleeding becomes very heavy, prolonged, or unusual for you, it is important to speak with your doctor.
How Mounjaro may improve polycystic ovary syndrome (PCOS) symptoms
In overweight women with PCOS, weight loss can lead to improvements in various hormonal and reproductive parameters, as well as improving PCOS symptoms. Benefits include reductions in insulin resistance and cardiovascular risk, as well as the restoration of regular menstrual cycles7. PCOS is strongly linked to insulin resistance, where the body does not respond properly to insulin. This can disrupt hormone balance and affect ovulation. Because Mounjaro improves insulin sensitivity and supports weight loss, it may help to reduce insulin resistance, improve hormone balance, restore more regular ovulation and make menstrual cycles more predictable4. Some women with PCOS find that weight loss and improved insulin control can support fertility and cycle regularity over time.
How Mounjaro may impact ovulation or fertility
Mounjaro itself is not a fertility treatment, but changes in weight, insulin levels, and hormone balance may influence ovulation. For some women, especially those with PCOS, improved metabolic health may lead to more regular ovulation and improved chances of pregnancy.
Contraception considerations
Mounjaro has been found to reduce the effectiveness of oral contraceptives5, so it is recommended to use a barrier method (e.g, condoms) in addition to oral contraceptive for 4 weeks after starting Mounjaro or increasing the dose6. Non-oral methods like the coil, implant, patch, or injection are not affected.
If you are planning to conceive, speak to your doctor or healthcare provider about when you should stop the medication, safe timing for pregnancy and alternative treatment options.
References
- Tirzepatide: A Systematic Update (2022) by Imma Forzano, Fahimeh Varzideh, Roberta Avvisato, ORCID, Stanislovas S, Jankauskas, Pasquale Mone and Gaetano Santulli
- Natural Cycles – Do GLP-1 weight loss drugs affect the menstrual cycle? [Online] https://www.naturalcycles.com/research-library/do-glp-1-weight-loss-drugs-affect-the-menstrual-cycle
- Nourish – How to get your period back after weight loss (2024). [Online] https://www.usenourish.com/blog/how-to-get-your-period-back-after-weight-loss#what-is-amenorrhea
- Role of Tirzepatide in Obesity Management Among Women with Polycystic Ovary Syndrome (2025) by Jannatul Ferdous, Muhammad Mobarock Hossain, Mst Jakanta Faika, Monowara Begum, Samira Mahjabeen, Iffat Ara Jahan, Mahira Zehreen Khan, Moktadir Mobarock Monsur Hossain. [Online] https://www.sciencepublishinggroup.com/article/10.11648/j.ijde.20251002.12
- Medicines and Healthcare products Regulatory Agency (2025) [Online]
https://www.gov.uk/government/news/women-on-skinny-jabs-must-use-effective-contraception-mhra-urges-in-latest-guidance - The Faculty of Sexual and Reproductive Healthcare – GLP-1 agonists and contraception (2025) [Online] https://www.cosrh.org/Common/Uploaded%20files/documents/Patient-information-GLP-1-agonists-and-contraception.pdf
- Endocrine and metabolic effects of GLP-1 receptor agonists on women with PCOS, a narrative review (2025) by Marine Monney, Maria Mavromati, Sophie Leboulleux and Karim Gariani. https://ec.bioscientifica.com/view/journals/ec/14/5/EC-24-0529.xml
