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
Free tracker included with every download this week
Can Mounjaro Stop Your Period?
Mounjaro (tirzepatide) can potentially affect your menstrual cycle, though this is not a common side effect. Some people taking this prescription weight loss injection have reported changes to their period, including irregular cycles or temporary cessation. However, individual experiences vary significantly. If you're concerned about menstrual changes whilst taking Mounjaro or considering starting this medication, it's important to discuss this with your GP or the prescriber conducting your clinical assessment. Changes in your cycle can also be related to gradual weight management itself, rather than the medication directly.
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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 vs Wegovy — Menstrual Effects Comparison
Both Mounjaro (tirzepatide) and Wegovy (semaglutide) are GLP-1-based weight loss injections licensed in the UK, though Mounjaro uses a dual GIP and GLP-1 mechanism whilst Wegovy activates GLP-1 alone. In clinical trials — SURMOUNT for Mounjaro and STEP for Wegovy — menstrual irregularities were reported by some participants, but neither medication specifically targets reproductive hormones. The primary cause of period changes is often the gradual weight management itself, not the injection. Hormonal changes during significant weight loss can temporarily affect menstruation, particularly in people with lower body fat percentages. Both medications require a UK prescription and clinical assessment before use. Neither medication is contraindicated during menstruation, but it's crucial to inform your prescriber of any menstrual concerns so they can assess whether the changes are medication-related, weight-loss-related, or indicative of another health issue.
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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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What to Do If Your Period Changes on Mounjaro
If you experience period changes whilst taking Mounjaro — such as missing a period, irregular bleeding, or changes in flow — contact your GP or prescriber promptly. Keep a brief log of any changes to help your healthcare provider assess the pattern. Missing periods (amenorrhoea) can occasionally signal other health issues, so medical evaluation is important. Your prescriber may adjust your dose, monitor your progress more closely, or refer you for further investigation. Remember that Mounjaro is a prescription-only medicine requiring ongoing clinical supervision; your GP can discuss whether continued use is appropriate for you. Additionally, if you're taking oral contraceptives, Mounjaro may reduce their absorption — your prescriber should have advised a barrier method for the first four weeks of treatment and after each dose increase. Use our free progress tracker to record not just weight changes but also any health observations, which you can share with your GP.
- 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.
Does Mounjaro cause period changes?
Mounjaro is not known to directly affect reproductive hormones, but some people report menstrual irregularities. This is more likely due to gradual weight management rather than tirzepatide itself. Individual responses vary. Contact your GP if you experience significant changes.
Is Mounjaro safe to use during your period?
Yes, Mounjaro can be used during menstruation. The injection does not interfere with your cycle and can be taken as scheduled. If you have severe period pain, discuss this with your GP to ensure it's unrelated to other health factors.
Can Mounjaro stop your period completely?
Whilst amenorrhoea (missing periods) is not a common side effect, it has been reported by some users. This is typically related to significant weight loss rather than the medication. Missing periods require medical evaluation as they can signal other health conditions. Contact your GP.
Does Wegovy affect your period like Mounjaro does?
Both medications work through similar appetite-regulating pathways. Whilst neither specifically targets hormones, both can be associated with period changes via weight loss effects. The frequency and severity are comparable, though individual experiences vary significantly.
Should I tell my prescriber about menstrual concerns before starting Mounjaro?
Yes, absolutely. Mention any history of menstrual irregularities, hormonal conditions, or concerns to your prescriber during your clinical assessment. This helps them monitor you appropriately and rule out other causes if changes occur during treatment.
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.