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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What Happens When You Stop Mounjaro
When you stop taking Mounjaro (tirzepatide), your body gradually returns to its natural appetite and metabolic state as the medication leaves your system. Understanding what to expect — and how this compares to stopping Wegovy — helps you plan your treatment journey. This guide covers the realistic timeline, potential weight regain, and the clinical differences between these two prescription weight loss medications available in the UK.
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Calculate Your BMI Instantly
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 Withdrawal Works vs Wegovy
When you stop your Mounjaro KwikPen injections, tirzepatide remains active in your body for approximately 4–5 weeks after your last dose, gradually declining. During this period, most people experience appetite returning gradually rather than suddenly. This differs from Wegovy (semaglutide), which has a slightly shorter half-life of about 1–2 weeks — meaning appetite typically returns faster after stopping a Wegovy prescription.
- Mounjaro's dual GIP and GLP-1 mechanism may extend the appetite-suppressing effect slightly longer than Wegovy's GLP-1-only action
- Individual variation is significant — some people notice appetite changes within days, others within weeks
- Weight regain typically follows a slow pattern initially, not immediate rebound
- Many people maintain part of their weight loss if they continue reduced-calorie eating and activity habits
Clinical evidence from SURMOUNT trials shows people who discontinued tirzepatide and didn't adopt sustained lifestyle changes often regained weight over 6–12 months. However, those who maintained diet and exercise patterns retained significant weight loss longer.
Clinically BackedWeight Loss
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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.
Managing the Transition and Regain Prevention
The key to minimising weight regain after stopping Mounjaro is maintaining the dietary and physical activity habits you built while on the medication. NHS guidance emphasises that weight loss injections are tools to support behaviour change, not replacements for lifestyle modification. When you stop, your GP or specialist can advise on transition strategies — some people gradually taper rather than stop abruptly, though this is not standard practice. Use our free GLP-1 weight loss calculator to understand what dose and timeline you're considering, and our BMI calculator to track your starting point and goals. Discussing timing and post-treatment plans with your prescriber before stopping ensures you have a realistic strategy for maintaining results.
- 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 I definitely regain weight when I stop Mounjaro?
Not necessarily. Weight regain depends on whether you maintain the eating and activity habits you developed while taking Mounjaro. Many people retain 50–70% of their weight loss if lifestyle changes persist. However, without ongoing effort, most people regain weight over 6–12 months as appetite returns to baseline.
How quickly does appetite come back after stopping Mounjaro?
Appetite typically returns gradually over 2–5 weeks as tirzepatide clears your system, not suddenly. Some people notice changes within days; others take several weeks. Individual variation is significant and depends on your metabolism, diet consistency, and activity levels.
Is stopping Mounjaro safer than stopping Wegovy?
Both are safe to stop — there are no dangerous withdrawal effects from either medication. Mounjaro may have a slightly longer washout period (4–5 weeks vs 1–2 weeks for Wegovy), but this doesn't make one inherently safer. Your prescriber will advise on timing based on your individual health.
Can I restart Mounjaro after stopping it?
Yes, you can restart Mounjaro if appropriate clinically. Your GP or prescriber will reassess your eligibility and health status. If restarting, you would typically begin with the starting dose (2.5 mg) and titrate up again, not resume at your previous dose.
Should I switch to Wegovy instead of stopping Mounjaro?
This is a prescriber decision. Both medications require ongoing prescription and clinical monitoring. If Mounjaro isn't working well or you're experiencing side effects, switching to Wegovy is possible — but this requires a new assessment and prescription from your GP or licensed prescriber.
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.