
Starting a new weight loss treatment can feel like a breakthrough - especially for women who have spent years struggling with PCOS, irregular cycles, or stubborn weight gain. Many people using GLP-1 medication describe renewed energy, steady progress on the scale, and a sense of hope. But alongside these benefits, some also notice unexpected changes in their menstrual cycle - such as new cramping, spotting, or shifts in flow.
It’s natural to wonder: Is this normal? Is it the medication, or just my body adjusting?
If you’ve had similar questions, you’re not alone. As more women turn to Mounjaro for weight management or type 2 diabetes, new conversations are opening up about its impact on menstrual health.
Changes in your cycle can feel unsettling, particularly when they appear alongside a new treatment. Whether it’s lighter or heavier bleeding, unfamiliar cramps, or questions about how Mounjaro may interact with hormones, contraception, or PCOS, it’s important to have clear, UK-specific information.
In this blog, we’ll explore how Mounjaro may affect the menstrual cycle, and share practical ways to manage symptoms and stay informed - so you can feel supported, not confused, as you move forward on your health journey.
Mounjaro works by mimicking two naturally occurring gut hormones - GLP-1 (glucagon-like peptide-1) and GIP (glucose-dependent insulinotropic polypeptide). Together, these hormones help to slow down gastric emptying, reduce appetite, improve insulin sensitivity, and lower blood glucose levels. While these effects are primarily targeted at metabolic regulation and weight loss, they also have indirect impacts on the hormonal systems that control the menstrual cycle.
For women, especially those with underlying hormonal conditions like polycystic ovary syndrome (PCOS), even small shifts in insulin levels, body weight, or inflammation can have a ripple effect on oestrogen balance, ovulation patterns, and menstrual symptoms. This means that although Mounjaro is not designed to act on reproductive hormones, its metabolic actions can influence menstrual health in meaningful ways.
One of the most significant ways Mounjaro may influence the menstrual cycle is through weight loss, which has a profound effect on hormonal balance. Body fat is not just stored energy, it’s hormonally active. Excess adipose tissue increases the production of oestrogen through a process called aromatisation.
When oestrogen levels are too high, it can disrupt the delicate hormonal interplay that governs the menstrual cycle, leading to irregular or absent periods, heavy bleeding, and painful cramps. By promoting steady and sustained weight loss, Mounjaro can help rebalance oestrogen levels, restoring hormonal equilibrium and contributing to more predictable menstrual patterns.
In addition to regulating oestrogen, healthy weight loss brings broader benefits to menstrual health. Studies have shown that losing weight can lead to more regular cycles, a reduction in PMS symptoms, and a decrease in systemic inflammation, which is a known contributor to period pain. Weight loss also significantly improves insulin sensitivity, a crucial factor for women with PCOS.
A 2025 clinical study in women with PCOS and obesity (n=56) found tirzepatide led to significant weight reduction (mean 9.54%) and improvement in menstrual regularity: irregular cycles decreased from 85.7% before treatment to 32.1% after. There was also a notable drop in prevalence of ovarian cysts and insulin resistance
For those living with PCOS - a condition that affects up to 1 in 10 women in the UK - Mounjaro’s impact can be particularly positive. By improving insulin resistance, one of the root causes of PCOS, Mounjaro can help restore more regular ovulation, reduce elevated androgen levels (which cause symptoms like acne, excess facial hair, and scalp hair thinning), and potentially enhance fertility. While not licensed specifically for PCOS in the UK, Mounjaro’s metabolic benefits can offer meaningful hormonal improvements for many women living with this condition.
Based on survey data from 1,754 users of GLP-1 medications (including tirzepatide) showed that 27% noticed changes in their menstrual cycles after starting treatment. Respondents with PCOS were even more likely to report changes (43%), with the most common being more predictable, more frequent, or shorter periods. However, rigorous clinical trial data specifically for tirzepatide remain limited
Despite anecdotal reports, there’s limited clinical trial data on Mounjaro’s direct impact on menstruation. Current studies haven’t flagged menstrual changes or cramps as common side effects. The MHRA and manufacturer’s patient information leaflets for Mounjaro in the UK do not list period changes as a primary or expected adverse effect.
However, real-world experiences from patients on forums and social media have started highlighting menstrual irregularities, delayed periods, or changes in cramp severity - pointing to a potential area for future research.
Although formal studies are currently limited, many women taking Mounjaro have shared a range of personal experiences on social media related to their menstrual cycle. Some report that their periods have become lighter and less painful, while others have noticed delayed cycles, spotting, or even more intense cramps during the initial adjustment phase. These changes may not be due to the medication directly, but rather indirect effects of weight loss, which can influence hormonal balance.
Fluctuations in oestrogen, insulin, and leptin levels - all of which are sensitive to changes in body weight and metabolic health - could contribute to these menstrual changes. Additionally, some of the side effects commonly associated with Mounjaro, such as nausea or abdominal discomfort, may overlap with or intensify typical menstrual symptoms, making it harder to distinguish the cause.
Mounjaro-induced weight loss can lower systemic inflammation - a major driver of dysmenorrhoea (painful periods).
Stabilising insulin and oestrogen levels may help with:
Could Mounjaro Make Cramps Worse?
While many women experience improvements in their menstrual symptoms with Mounjaro, it’s also possible for some to notice a temporary worsening of cramps or cycle disturbances. This can happen for several reasons. Rapid weight loss, especially in the early stages of treatment, can place stress on the body and temporarily disrupt hormonal balance, leading to more intense cramps or irregular periods. Additionally, as the body undergoes hormonal fluctuations during weight loss, menstrual cycles may become less predictable for a time.
Another important factor to consider is that Mounjaro slows gastric emptying, which may affect how oral medications are absorbed - including combined oral contraceptive pills and oral HRT. If the absorption of these hormones is reduced, hormone levels in the body may drop, potentially causing breakthrough bleeding, spotting, or a return of menstrual symptoms such as cramping or irregular flow. This is particularly relevant for women who rely on these medications for menstrual regulation or symptom control and highlights the importance of discussing contraceptive or HRT options with a healthcare provider when starting Mounjaro.
Mounjaro can cause:
These may overlap with PMS symptoms, making it harder to distinguish between side effects and menstrual pain.
For women using Mounjaro, there are several important factors to consider when it comes to menstrual health, contraception, and hormone therapy. One of the key concerns is how Mounjaro may affect the absorption of oral medications due to its action of slowing gastric emptying. This can potentially reduce the effectiveness of oral contraceptive pills, putting users at risk of unintended pregnancy.
Current guidance suggests using a barrier method, such as condoms, for at least four weeks after starting Mounjaro and for four weeks after each dose increase. Alternatively, women may wish to speak to their GP about switching to non-oral forms of contraception, such as patches, IUDs, or implants, which are not affected by changes in digestion.
Women taking hormone replacement therapy (HRT) during the perimenopausal or menopausal period should be aware that oral HRT may also be impacted. The British Menopause Society advises considering transdermal options, like patches or gels, which bypass the digestive system and maintain more stable hormone levels. In some cases, adjusting the dose of oral progesterone may be necessary, but this should only be done in consultation with a healthcare provider.
Tracking your menstrual cycle becomes particularly important while on Mounjaro. Noting changes in cycle length, flow, cramping, mood swings, or energy levels can help identify any emerging patterns or concerns. You should seek medical advice if you experience significant changes, such as missed periods, unusually heavy or light bleeding, persistent or worsening cramps, or unexpected spotting - especially if you're on HRT or haven’t had periods for some time. These could signal hormonal imbalances, medication side effects, or other underlying issues that need attention. Use apps like Clue or Flo, or simply note symptoms in a calendar.
Managing menstrual symptoms while on Mounjaro involves a holistic approach that supports both hormonal balance and overall wellbeing.
1. Supportive Lifestyle Habits
Start by focusing on lifestyle habits that naturally ease period discomfort. A balanced diet rich in whole grains, leafy greens, lean proteins, and healthy fats can help stabilise blood sugar levels and reduce inflammation - both of which may play a role in period cramps and mood changes. Including foods high in magnesium (like nuts, seeds, and dark chocolate) and omega-3 fatty acids (like salmon or flaxseeds) may also help reduce cramping.
Staying physically active is another powerful tool - gentle exercises like walking, stretching, or yoga can increase blood flow, reduce tension, and improve your overall sense of wellbeing during your cycle. Hydration and adequate sleep support hormone regulation and can ease fatigue and bloating, while stress-reducing activities like meditation, journaling, or even warm baths may help ease both mental and physical premenstrual symptoms.
2. Pain Relief Options
For pain relief, over-the-counter medications such as paracetamol or ibuprofen can be effective in managing cramps. However, it’s important to use them cautiously if you’re experiencing gastrointestinal side effects from Mounjaro like nausea or constipation.
3. Complementary Therapies
Some people also find comfort in non-pharmacological methods like applying a hot water bottle to the lower abdomen, using herbal teas like chamomile or ginger, or taking magnesium supplements - though any supplement should be discussed with your GP to ensure it's safe alongside your current medications.
4. Communicate with Your Healthcare Provider
Lastly, open communication with your healthcare provider is essential. If your cycle becomes irregular, if cramps worsen, or if you experience any unexpected symptoms such as spotting, prolonged bleeding, or missed periods, it’s important to seek professional advice. Your doctor can help determine whether these changes are related to Mounjaro, weight loss, hormonal shifts, or another underlying cause, and guide you on the best course of action.
Mounjaro is a powerful medication with proven benefits for weight loss and metabolic health. For many women, these benefits may translate into more regular and less painful periods, especially for those with PCOS or insulin resistance. However, it’s essential to understand that period changes are not officially listed as side effects but do occur anecdotally. Menstrual cramps may improve or worsen depending on your hormonal baseline and weight loss pace. Mounjaro can affect hormonal contraceptives and HRT absorption, which requires additional precautions. Being proactive, tracking your cycle, choosing the right contraceptives, and staying in touch with your GP, ensures that you can reap the benefits of Mounjaro without sacrificing menstrual health.
Weight loss journeys are about more than numbers on a scale. For women, especially, they often involve complex hormonal shifts.
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