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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How Long Can You Be On Mounjaro?
Mounjaro (tirzepatide) can be used for as long as it remains clinically effective and well-tolerated — there is no set time limit for remaining on the medication in the UK. Most people continue treatment for months or years, adjusting doses as needed. However, duration depends on individual response, health goals, and ongoing clinical review. Your prescriber will assess whether continued treatment remains appropriate during regular check-ins. Unlike some weight loss medications, Mounjaro treatment is not time-restricted, though ongoing suitability is regularly reviewed.
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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: Treatment Duration & Mechanism Differences
Both Mounjaro and Wegovy are designed for long-term weight management with no predetermined end date — they continue as long as they are helping and remain tolerated. The key difference lies in their mechanism: Mounjaro is a dual GIP and GLP-1 receptor agonist, whereas Wegovy is a GLP-1-only agonist. This dual mechanism in Mounjaro may provide additional appetite suppression benefits, though clinical trial outcomes show both medications produce meaningful weight loss. SURMOUNT trial data showed Mounjaro users lost approximately 15–21% of body weight over 72 weeks at maximum dose (15 mg), while STEP trial data for Wegovy showed approximately 14.9% average loss over 68 weeks. Individual responses vary significantly. Neither medication is a one-off treatment — both require ongoing commitment and regular clinical monitoring via your prescriber, whether through NHS specialist services or private prescription pathways in the UK.
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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.
Free Weight Loss Tools & Guides
Everything you need to understand your weight, explore medication options, and track your progress — completely free.
Duration, Discontinuation, and Individual Suitability
Treatment duration with Mounjaro or Wegovy is individualised. Some people continue for years, others may pause or stop if weight loss goals are reached or if side effects become problematic. Important: stopping suddenly is not recommended — doses are typically reduced gradually under prescriber guidance. Weight regain often occurs after stopping either medication, so many people restart or continue long-term. Both medications require regular clinical assessment to confirm suitability continues. Your GP or prescriber will review your progress, side effects, blood pressure, and blood sugar control periodically. If you develop contraindications (such as pregnancy planning or gallbladder problems), treatment may need to stop. Try our free BMI calculator and GLP-1 weight loss calculator to understand your baseline and projected outcomes before discussing long-term treatment options with your prescriber.
- 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 you stay on Mounjaro indefinitely?
Yes, Mounjaro can be used long-term with no predetermined end date, provided it remains clinically effective and well-tolerated. However, your prescriber will review suitability regularly. If weight loss plateaus, side effects become unmanageable, or your health circumstances change, treatment may be adjusted or stopped. Long-term safety data continues to accumulate — discuss ongoing use at each clinical review.
Is Mounjaro duration different from Wegovy duration?
No — both Mounjaro and Wegovy can be used long-term without a set time limit. The difference is mechanism (Mounjaro uses dual GIP+GLP-1, Wegovy uses GLP-1 only) and average weight loss in trials. Duration depends on individual response and ongoing clinical need, not the medication choice itself.
What happens if you stop Mounjaro suddenly?
Stopping suddenly is not recommended. Doses should be reduced gradually under prescriber guidance to minimise side effects. After stopping, weight regain often occurs within months — many people find long-term continuation or restarting necessary to maintain loss. Always discuss stopping plans with your prescriber.
How often is Mounjaro reviewed by a prescriber?
UK prescribers typically review Mounjaro every 4–12 weeks initially, then at least every 6–12 months long-term. Reviews assess weight loss progress, side effects, blood pressure, blood sugar, and overall suitability. More frequent reviews may be needed if doses are changing or side effects emerge.
Can you switch between Mounjaro and Wegovy during treatment?
Switching is possible but must be managed by your prescriber — there is no direct dose equivalence between the two. Approximate conversions exist (e.g., Mounjaro 10 mg ≈ Wegovy 1.7 mg) but switching requires clinical guidance. Your prescriber will advise if switching is appropriate for your situation.
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.