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
How Long Can You Be On Mounjaro?
Mounjaro (tirzepatide) is a prescription-only weight management injection licensed in the UK, but there's no fixed time limit for how long you can take it. Treatment duration depends on your individual health, weight loss goals, and how well you're responding. Most people continue as long as it's helping them lose weight and they're tolerating it well. Your GP or prescriber will review your progress regularly and discuss whether to continue, adjust your dose, or stop treatment based on your circumstances.
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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 Long Do People Typically Take Mounjaro?
In clinical trials like SURMOUNT-1, participants took Mounjaro for up to 72 weeks (approximately 17 months), and most continued to lose weight throughout this period. However, real-world treatment can continue much longer. There is no maximum duration specified in UK guidance — some people may take it for 1–2 years, others may continue indefinitely if they remain eligible and it continues to work.
The key factor is ongoing clinical benefit. If you're still losing weight, maintaining weight loss, or experiencing health improvements (better blood sugar control, reduced blood pressure), your prescriber is likely to continue your treatment. If you've plateaued for several months with no further progress, your GP may discuss whether to continue, change your approach, or consider stopping.
- Regular review appointments (typically every 3–6 months) assess your progress
- Dose adjustments may be made if needed to continue results
- If side effects become intolerable, your prescriber may pause or stop treatment
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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.
Stopping Mounjaro — What Happens Next?
When you stop taking Mounjaro, the medication leaves your system within approximately 4–5 weeks (the time it takes for one weekly injection to clear). Weight regain is common after stopping unless lifestyle changes (diet and physical activity) continue. NHS guidance emphasises that weight loss medications work best when combined with sustained behavioural changes.
Your GP may recommend a plan before stopping — for example, stepping down to a lower dose first, or transitioning to another supported approach. Some people may restart Mounjaro later if weight returns and they remain eligible. The decision to continue, pause, or stop is always made with your prescriber based on your individual health needs, not on a fixed time schedule.
- 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.
Is there a time limit on how long I can take Mounjaro?
No. There is no maximum duration specified in UK guidance. Treatment continues as long as you're eligible, tolerating it well, and experiencing clinical benefit. Your GP reviews your progress regularly to decide whether to continue, adjust your dose, or stop based on your individual response.
What happens if I stop taking Mounjaro?
The medication clears your system within 4–5 weeks. Weight regain is common unless you maintain diet and exercise changes. Discuss a stopping plan with your prescriber first — you may benefit from stepping down gradually rather than stopping abruptly.
Can I take Mounjaro long-term?
Yes, you can take Mounjaro long-term if you remain eligible and it continues to help. Some people take it for several years. However, long-term use requires regular appointments with your GP or prescriber to monitor effectiveness, side effects, and overall health.
How often will my GP review my Mounjaro treatment?
NHS guidance recommends review appointments every 3–6 months during treatment. Your prescriber will assess weight loss progress, side effects, health improvements, and whether to continue, adjust the dose, or consider stopping based on your circumstances.
What's the difference between Mounjaro and Wegovy for treatment duration?
Both are licensed for long-term weight management with no fixed maximum duration. Mounjaro (tirzepatide) is a dual GIP/GLP-1 agonist; Wegovy (semaglutide) is a GLP-1 agonist only. Treatment length depends on individual response, not on the medication itself. Use our GLP-1 weight loss calculator to compare potential outcomes.
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.