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
Do People Put Weight Back On After Mounjaro?
Yes, some people do regain weight after stopping Mounjaro — but this isn't inevitable. Weight regain depends heavily on whether lifestyle changes become permanent. Clinical evidence shows that stopping a weekly weight loss injection without maintaining reduced calorie intake and physical activity often leads to weight return. However, many people successfully keep weight off long-term by building sustainable eating habits during treatment. Your GP can discuss strategies to help prevent rebound weight gain.
10,000+ calculations today · NHS-aligned thresholds · 100% free
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.
What the Evidence Shows About Weight Regain
Clinical trials of Mounjaro (tirzepatide), the dual GIP and GLP-1 receptor agonist injection, show that weight regain occurs when the medication is stopped and lifestyle changes aren't maintained. In the SURMOUNT trials, participants who lost weight on Mounjaro and then stopped the medication experienced some weight rebound over the following months — typically losing 30–50% of their weight loss within the first year off treatment.
This pattern is consistent across weight loss medications: the injection itself isn't a permanent fix; it's a tool that works best alongside reduced-calorie diet and increased physical activity. People who continue healthy eating and exercise habits after stopping Mounjaro are significantly more likely to maintain their weight loss than those who return to previous behaviours. The UK prescription weight loss pathway emphasises this — medication is prescribed alongside lifestyle support, not instead of it. Our GLP-1 weight loss calculator can help you understand realistic expectations for your own situation.
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.
How to Reduce the Risk of Weight Regain After Mounjaro
The key to preventing weight regain after stopping Mounjaro is building sustainable lifestyle habits during treatment. While taking the KwikPen injection, you're typically eating less and moving more — use this time to establish new eating patterns, food preferences, and activity routines that feel natural rather than restrictive. Many people find that their appetite naturally stabilises after being on Mounjaro for several months.
Work with your GP or a dietitian before stopping treatment to create a practical maintenance plan. Some people benefit from transitioning to ongoing support through NHS tier 3 weight management services or private coaching. Others successfully maintain by using tools like our free progress tracker to monitor weight trends early and adjust diet or activity if modest regain begins. Regular physical activity (aim for 150 minutes weekly per NHS guidance) is particularly protective against rebound weight gain across all research evidence.
- 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.
What percentage of weight comes back after stopping Mounjaro?
Evidence suggests 30–clinically studied weight loss may return within the first year if lifestyle changes aren't maintained. However, this varies significantly. People who continue healthy eating and exercise often maintain most of their loss. Individual factors including genetics, starting weight, and how long you were on treatment all affect rebound risk. Your GP can discuss your personal risk factors.
Should I stay on Mounjaro forever to keep weight off?
Not necessarily. Mounjaro is prescription-only and prescribed for a defined treatment period, usually 1–2 years. The goal is to use the medication to build sustainable habits you can maintain independently. Some people do continue long-term if benefits outweigh side effects and costs. This is a discussion for your prescriber based on your individual health and response.
Can I restart Mounjaro if I regain weight after stopping?
Potentially, yes — but restarting requires a new clinical assessment from your prescriber. You'd need to demonstrate that your regain is significant and that you're motivated to re-engage with lifestyle changes. NHS eligibility criteria and private prescriber standards would apply again. It's not typically prescribed as an on-and-off cycle.
How long does it take to regain weight after stopping?
Weight regain typically occurs gradually over weeks to months rather than all at once. Most rebound happens in the first 3–6 months after stopping the weekly weight loss injection. Monitoring your weight regularly using our progress tracker can help you spot trends early and adjust diet or activity before significant regain occurs.
Does exercise alone prevent weight regain after Mounjaro?
Exercise is protective but usually isn't enough on its own. Research shows that maintaining weight loss after stopping medication requires both continued reduced calorie intake AND regular physical activity. People who exercise but return to previous eating patterns typically still regain weight. Both diet and activity matter equally.
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.