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?
Yes, Mounjaro can potentially affect your menstrual cycle, including stopping your period or causing irregular bleeding. This happens because gradual weight management affects hormones that regulate menstruation. If you're considering Mounjaro (tirzepatide) and have concerns about your period, understanding how to access it in the UK—both cost and eligibility—is important. This guide covers menstrual effects, access routes, and what to expect when starting a GLP-1 or dual GIP/GLP-1 weight loss injection.
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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.
How Mounjaro Affects Your Period and UK Access Routes
Mounjaro can disrupt your menstrual cycle because gradual weight management alters oestrogen levels and affects the hormones that regulate ovulation and bleeding. This is not unique to Mounjaro—any significant weight loss, including from diet and exercise, can cause similar changes. Your period may become lighter, irregular, heavier, or stop temporarily (amenorrhoea). These changes are usually reversible once your weight stabilises. In the UK, you can access Mounjaro through two main routes: NHS specialist weight management services (tier 3) or private online consultation with a UK-licensed prescriber. NHS access typically involves referral from your GP and assessment by a specialist multidisciplinary team, though waiting lists vary significantly by region. Private access is faster—usually within days—but costs between £129–£320 per month depending on the dose (2.5 mg to 15 mg weekly). Both routes require a clinical assessment to confirm eligibility: BMI of 30 or above, or 27–29.9 with weight-related health conditions such as type 2 diabetes, hypertension, or sleep apnoea.
Clinically BackedWeight Loss
No appointments. No waiting rooms. Just care — from a UK-regulated online pharmacy.
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.
Free Weight Loss Tools & Guides
Everything you need to understand your weight, explore medication options, and track your progress — completely free.
NHS vs Private Mounjaro Prescription—Cost, Timeline, and How to Apply
NHS route: Free once prescribed through a specialist service, but availability is limited and waiting lists can be months or longer depending on your ICB (integrated care board) region. Your GP must refer you to tier 3 weight management services first. Not all areas fund tirzepatide yet, so availability varies. Private route: Faster access (typically 24–48 hours), no waiting list, and available without NHS referral. Online consultations cost £0–£30, and prescriptions are dispensed by a GPhC-registered pharmacy. You can use our free GLP-1 weight loss calculator to explore potential outcomes at different doses before committing. Both routes require you to be 18+, not pregnant or breastfeeding, and have no contraindications. Your prescriber will assess whether Mounjaro is suitable for your individual health, including menstrual health concerns.
- 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.
Will Mounjaro definitely stop my period?
No, not everyone experiences menstrual changes on Mounjaro. Some people see no effect, whilst others experience lighter, irregular, or stopped periods. gradual weight management—regardless of cause—can disrupt hormones that regulate ovulation. This is usually temporary and reverses as your weight stabilises. Always discuss period concerns with your GP or prescriber before starting.
How much does Mounjaro cost privately in the UK?
Private Mounjaro typically costs £129–£320 per month depending on your dose (starting at 2.5 mg, escalating to a maximum of 15 mg weekly). Each KwikPen contains 4 weekly doses. Costs vary slightly between providers. Online consultation fees are usually £0–£30. Always ask the provider about their full costs before starting.
Can I get Mounjaro free on the NHS in the UK?
Yes, if you're approved by a specialist tier 3 weight management service. However, NHS availability is limited and varies significantly by region. Your GP must refer you to your local service first. Waiting lists can be several months to over a year in many areas. Check with your GP about availability in your ICB region.
What's the difference between Mounjaro and Wegovy for menstrual changes?
Both Mounjaro (tirzepatide) and Wegovy (semaglutide) can affect your period because both cause weight loss that alters hormones. Mounjaro is a dual GIP/GLP-1 agonist; Wegovy is a GLP-1 agonist only. Clinical trials don't show a significant difference in menstrual disruption between the two—the effect depends on your individual response and rate of weight loss, not the medication type.
How do I apply for Mounjaro through the NHS?
Ask your GP for a referral to your local tier 3 weight management service. Your GP will assess whether you meet eligibility criteria (BMI ≥30, or BMI 27–29.9 with weight-related conditions). If eligible, you'll be added to the specialist service's waiting list and invited for a multidisciplinary assessment. From there, a prescriber will decide if Mounjaro is appropriate for you. Timelines vary from months to over a year depending on your region.
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.