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 Affect Your Menstrual Cycle?
Mounjaro (tirzepatide) is a prescription-only GLP-1 and GIP receptor agonist used for weight management in the UK. Women taking Mounjaro have reported changes to their menstrual cycle, including irregular periods, lighter or heavier bleeding, or temporary changes in cycle length. These changes are not listed as official side effects in the product information, but they are documented in clinical experience and patient reports. Understanding what to expect can help you make an informed decision with your GP or prescriber about whether Mounjaro is right for you.
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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.
What Does the Evidence Show About Mounjaro and Periods?
Clinical trials for Mounjaro (tirzepatide) did not specifically measure menstrual cycle changes, so official data is limited. However, gradual weight management itself can affect hormonal balance and menstrual regularity — a phenomenon well-documented in medical literature. When you lose weight quickly, oestrogen levels can fluctuate because oestrogen is partly stored in body fat. This can lead to irregular periods, lighter bleeding, or temporary amenorrhoea (missed periods).
Additionally, some women report that GLP-1 and GIP receptor agonists may directly influence appetite hormones and gut function, which can indirectly affect menstrual hormones. Stress reduction — which often accompanies successful weight loss — can also help normalise cycle patterns. Most menstrual changes reported with weight loss medications are temporary and resolve within a few months as your body adjusts.
If you experience significant menstrual changes whilst taking Mounjaro, contact your GP or prescriber. Sudden or severe changes warrant medical review.
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How It Works
Three simple steps to understand your weight and take action.
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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Accessing Mounjaro in the UK: NHS vs Private Routes
NHS access: Mounjaro is available through NHS specialist tier 3 weight management services. You must be referred by your GP and meet eligibility criteria (BMI ≥30, or BMI ≥27.5 with weight-related health conditions). NHS availability varies significantly by region, and waiting lists can be lengthy.
Private access: Available through GPhC-registered online prescribers following a clinical assessment. No NHS referral required. Private prescriptions typically cost £120–£300 per month depending on dose. An online consultation assesses your medical history, current medications, and suitability. If approved, your prescription is dispensed by a registered pharmacy.
Both routes require a clinical assessment before prescription. Your prescriber will discuss menstrual changes and other potential side effects, and can monitor you throughout treatment. Use our free GLP-1 weight loss calculator to explore potential outcomes, or check your BMI using the calculator on this page.
- 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.
Can Mounjaro stop or delay your period?
Weight loss itself can temporarily affect menstrual regularity. Some women report delayed or missed periods when taking Mounjaro, though this is not an official listed side effect. This usually resolves within a few months as your body adjusts. If your period is absent for more than three months, contact your GP.
Is it safe to take Mounjaro if you're trying to conceive?
No. Mounjaro is not recommended if you're planning to become pregnant. If you become pregnant whilst taking Mounjaro, stop immediately and contact your GP. Women taking oral contraceptives should use a barrier method for 4 weeks after starting Mounjaro and 4 weeks after each dose increase, as Mounjaro may reduce oral medication absorption.
Will my period return to normal after stopping Mounjaro?
Yes, in most cases. Menstrual cycles typically normalise within a few months after stopping Mounjaro, particularly if your weight stabilises. Hormonal balance usually returns as oestrogen levels adjust. If your cycle doesn't normalise within 3–6 months, discuss this with your GP.
Should I tell my prescriber about menstrual changes?
Absolutely. Always inform your prescriber or GP of any menstrual changes — lighter or heavier bleeding, irregular cycles, or missed periods. This helps them assess whether changes are weight-loss-related or potentially due to another factor. Your GP can provide personalised advice and monitor your health.
Does Mounjaro affect hormone levels?
Mounjaro itself doesn't directly alter reproductive hormones, but gradual weight management does. Since oestrogen is stored in body fat, losing weight quickly can lower oestrogen temporarily, affecting menstruation. This is a normal metabolic response and usually resolves as weight stabilises. GLP-1 medications also affect gut hormones, which may indirectly influence overall hormonal balance.
Ready to take control of your weight loss journey?
Start with a free BMI check, explore your GLP-1 options, or begin tracking your progress today. No sign-up. No cost. Just results.