The UK's most complete GLP-1 guide
Every Question Answered. Every Side Effect Explained.
- How GLP-1 medications work
- Mounjaro vs Wegovy compared
- Injection instructions
- Side effects & solutions
- What to eat on treatment
- FAQs answered
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Does Mounjaro Cause Period Cramps?
Period cramps and menstrual changes are recognised side effects that some women experience when taking Mounjaro (tirzepatide). While not everyone will experience them, understanding what to expect and when to seek advice from your GP is important if you're considering this prescription-only weight management injection. This guide explains what the evidence shows, when symptoms typically occur, and how the NHS approaches managing these effects alongside your treatment.
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Enter your height and weight below. Supports both imperial (stone & lbs) and metric (kg). Results include NHS category, healthy weight range, and ethnicity adjustments.
What Is BMI and Why Does It Matter?
Body Mass Index (BMI) is the most widely used screening tool for assessing whether your weight falls within a healthy range. Used by the NHS, GPs, and weight management services across the UK, BMI provides a quick snapshot of your weight relative to your height. The formula is simple: your weight in kilograms divided by your height in metres squared (kg/m²).
While BMI isn't a perfect measure — it doesn't account for muscle mass, bone density, or fat distribution — it remains the standard first step in identifying potential weight-related health risks including type 2 diabetes, cardiovascular disease, high blood pressure, and certain cancers.
The NHS also recommends adjusted thresholds for people of South Asian, Chinese, or Black African heritage — a BMI of 23 or above is classified as overweight, and 27.5 as obese. Our calculator includes this adjustment as a one-click toggle.
Mounjaro and Menstrual Side Effects — What the Evidence Shows
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist — a once-weekly injection licensed in the UK for weight management in adults. During clinical trials and post-marketing use, some women have reported menstrual changes including period cramps, irregular cycles, heavier or lighter periods, and delayed menstruation.
These effects are thought to relate to gradual weight management itself rather than the medication directly. When your body loses weight quickly, hormonal changes can affect your menstrual cycle. However, because Mounjaro affects stomach emptying and appetite regulation, some women also report nausea or digestive changes that can exacerbate cramping sensations.
The good news: menstrual changes during weight management treatment are typically temporary. Most women find their cycle stabilises within 2–3 months as their body adjusts, or once weight loss stabilises. Keep a brief record of any changes and discuss these with your GP, who can provide reassurance and, if needed, suggest symptom management strategies.
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Enter your height and weight in our free calculator. Get your BMI, NHS category, healthy weight range, and ethnicity-adjusted thresholds instantly.
If your BMI suggests you're overweight or obese, explore our GLP-1 calculators to project potential weight loss on Mounjaro or Wegovy.
Use our progress tracker to log your weight weekly, visualise your journey with charts, and stay motivated — all stored privately in your browser.
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When to Contact Your GP About Period Cramps on Mounjaro
Contact your GP if you experience severe or persistent cramping that doesn't improve with over-the-counter pain relief, sudden changes in your cycle (especially if you've had regular periods previously), or if cramps are accompanied by unusual vaginal bleeding, fever, or severe abdominal pain spreading to your back — these could indicate pancreatitis, a rare but serious side effect requiring immediate attention.
Your GP can rule out other causes, recommend pain relief options safe to take alongside Mounjaro, and advise whether continuing the medication is appropriate for you. They can also discuss whether a slower dose titration might reduce overall side effects. Don't assume cramping will definitely occur — many women take Mounjaro without menstrual changes at all. Individual responses vary significantly.
- Dual GIP/GLP-1 receptor agonist
- Up to 22.5% body weight loss (SURMOUNT-1)
- Weekly injection, dose escalation over 20+ weeks
- Available via private prescription in the UK
- Doses: 2.5mg → 5mg → 7.5mg → 10mg → 12.5mg → 15mg
- GLP-1 receptor agonist
- Up to 15–17% body weight loss (STEP trials)
- Weekly injection, 5-step dose escalation
- NHS & private prescription available
- Doses: 0.25mg → 0.5mg → 1mg → 1.7mg → 2.4mg
Mounjaro vs Wegovy: Head-to-Head
A side-by-side comparison of the two most popular GLP-1 weight loss medications available in the UK.
| Feature | Mounjaro | Wegovy |
|---|---|---|
| Drug class | Dual GIP/GLP-1 agonist | GLP-1 agonist |
| Active ingredient | Tirzepatide | Semaglutide |
| Avg. weight loss | 15–22.5% | 12–17% |
| Key trial | SURMOUNT-1 (2022) | STEP 1 (2021) |
| Max dose | 15 mg weekly | 2.4 mg weekly |
| Escalation period | 20–32 weeks | 16–20 weeks |
| Administration | Weekly injection (pen) | Weekly injection (pen) |
| NHS availability | Private prescription only | NHS & private |
| Approx. private cost | £150–£250/month | £150–£300/month |
| Common side effects | Nausea, diarrhoea, constipation | Nausea, vomiting, diarrhoea |
Data sourced from SURMOUNT-1 and STEP 1 clinical trials. Costs are approximate and vary by provider. Always consult a prescriber.
Am I Eligible for Weight Loss Medication?
In the UK, eligibility for GLP-1 weight loss medications like Mounjaro and Wegovy is based on your BMI and overall health profile.
- BMI of 30 or above (obese)
- Age 18 or over
- No contraindicated conditions
- Committed to lifestyle changes
- BMI of 27 or above
- Plus type 2 diabetes
- Or high blood pressure
- Or obstructive sleep apnoea
Use our BMI calculator to check whether your BMI falls within the eligible range.
How We Built These Tools
Every calculator and guide on myweightcheck is built with accuracy and transparency in mind. Our BMI calculator uses the standard WHO formula with NHS-aligned category thresholds. Our GLP-1 projections are modelled on published clinical trial data from SURMOUNT and STEP studies.
All data stays on your device. We don't require sign-ups, and we don't store your health information on any server. Your progress tracker saves data locally in your browser using localStorage, so only you can see it.
We're based in the UK and our tools are designed specifically for UK users — supporting stone & lbs by default, referencing NHS guidelines, using NICE-approved medication data, and linking to GPhC-registered pharmacies.
Frequently Asked Questions
Common questions about BMI, weight loss medications, and our free UK tools.
Is period cramping a common side effect of Mounjaro in the UK?
Period cramps and menstrual changes are reported by some women taking Mounjaro, but are not listed as "very common" side effects (affecting more than 1 in 10). They are more common with gradual weight management generally. If you experience cramping, contact your GP to discuss whether it's related to the medication or weight loss itself.
Can I take paracetamol or ibuprofen for period cramps while on Mounjaro?
Paracetamol (paracetamol-based products like Panadol) is generally safe to take alongside Mounjaro. Ibuprofen may be used but discuss with your GP first, especially if you have any stomach sensitivity. NSAIDs can occasionally interact with gradual weight management. Your GP can recommend the safest option for you personally.
Will my period return to normal after stopping Mounjaro?
Yes, for most women. Menstrual cycle changes associated with Mounjaro typically resolve within 2–3 months of stopping the medication or once weight stabilises. However, if you've experienced prolonged irregular periods, discuss this with your GP to rule out other causes and monitor your cycle recovery.
Does Mounjaro affect contraceptive pill effectiveness if I get period cramps?
Yes — importantly, Mounjaro can reduce how well your body absorbs oral contraceptives because it slows stomach emptying. If taking the pill, your prescriber will advise using additional contraception (like condoms) for 4 weeks after starting Mounjaro and after each dose increase. Period changes may also be more noticeable because of this interaction.
Should I stop Mounjaro if I develop severe period cramps?
Don't stop without speaking to your GP first. Severe cramping may improve as your body adjusts, or your GP might recommend a slower dose titration, pain management strategies, or investigation for other causes. Your prescriber needs to assess your individual situation before any changes to your treatment.
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