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 Do People Stay on Mounjaro?
There's no fixed timeframe for how long people stay on Mounjaro (tirzepatide). Treatment duration varies significantly between individuals and depends on personal health goals, weight loss progress, and how well the medication suits you. Most people in clinical trials remained on Mounjaro for at least 68 weeks, though some continue longer. Your GP or prescriber will review whether continued treatment is right for you based on your individual results and health needs.
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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.
Treatment Duration and Maintenance Phases
Mounjaro is not typically a short-term treatment. Unlike some weight loss approaches, tirzepatide is designed as an ongoing therapy for people managing their weight long-term. In the SURMOUNT-1 clinical trial, participants stayed on Mounjaro for 72 weeks (approximately 17 months), with most continuing through to the end of the trial period. After reaching your target dose (usually 15 mg once weekly), you enter a maintenance phase where the dose remains stable while you continue to lose weight and manage your appetite.
- Initial phase: 4–20 weeks (dose escalation from 2.5 mg to 15 mg)
- Maintenance phase: ongoing, typically 12 months or longer
- Review phase: your prescriber will assess progress at regular intervals (usually 3–6 months)
Weight loss typically continues throughout the maintenance phase as your body adapts to the medication and you sustain lifestyle changes like reduced-calorie diet and increased physical activity.
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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.
What Happens When You Stop Mounjaro
If you stop taking Mounjaro, weight regain can occur relatively quickly. Clinical evidence suggests that people who discontinue tirzepatide may regain a significant proportion of lost weight within weeks to months. This is why Mounjaro is often described as a long-term treatment rather than a temporary intervention. Your prescriber may recommend continuing Mounjaro indefinitely if it's working well and you have no contraindications, or they may suggest a planned stop-and-review if your weight and health goals have been achieved and maintained through lifestyle changes alone. Any decision to stop should be made with your GP or specialist, never abruptly.
If you stop taking Mounjaro, weight regain can occur relatively quickly. Clinical evidence suggests that people who discontinue tirzepatide may regain a significant proportion of lost weight within weeks to months. This is why Mounjaro is often described as a long-term treatment rather than a temporary intervention. Your prescriber may recommend continuing Mounjaro indefinitely if it's working well and you have no contraindications, or they may suggest a planned stop-and-review if your weight and health goals have been achieved and maintained through lifestyle changes alone. Any decision to stop should be made with your GP or specialist, never abruptly. Use our free GLP-1 weight loss calculator to explore how long-term treatment at different doses may support your weight management goals.
- 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.
How long does it take to see results on Mounjaro?
Most people notice appetite reduction within 1–2 weeks of starting. Measurable weight loss typically becomes visible after 4–8 weeks. More significant weight loss usually appears after 12–16 weeks once you've reached a therapeutic dose. Results vary based on dose, lifestyle changes, and individual metabolism.
Can you take Mounjaro forever?
There's no defined maximum duration. Mounjaro can be used long-term if it continues to be effective and you tolerate it well. However, ongoing clinical review with your GP or prescriber is essential. Some people may eventually stop, while others may continue indefinitely as part of their weight management strategy.
What happens if I miss doses of Mounjaro?
Missing occasional doses can slow your weight loss progress. If you miss your weekly injection by more than 4 days, skip that dose and continue your normal schedule. Never take a double dose. Consistent use helps maintain appetite control and steady weight loss results.
How often will my GP review my Mounjaro treatment?
Most prescribers review Mounjaro use every 3–6 months initially, then annually if treatment is stable. Your GP will check weight loss progress, side effects, and whether continued treatment remains appropriate. NHS NICE guidance recommends regular monitoring throughout treatment.
Is Mounjaro the same as Wegovy?
No. Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, while Wegovy (semaglutide) is a GLP-1 agonist only. Both are once-weekly injections licensed for weight management in the UK, but they work through different mechanisms. Your prescriber will assess which is more suitable for you based on your individual health profile.
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.