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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Gaining Weight After Mounjaro — What You Need to Know
Some people experience weight regain after stopping Mounjaro or reducing their dose, even when they initially lost weight successfully. This is a common concern for patients using this weekly weight loss injection. Understanding why this happens — and what you can do about it — helps you make informed decisions about your weight management journey with your GP or prescriber.
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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.
Why Weight Regain Happens After Mounjaro
When you stop taking Mounjaro (tirzepatide), or reduce your dose, the medication's effects gradually wear off over several days to weeks. Mounjaro works as a dual GIP and GLP-1 receptor agonist, which means it reduces appetite, slows stomach emptying, and helps you feel fuller. Without these hormonal signals, your natural appetite can return to pre-treatment levels.
Weight regain is not a failure — it reflects how your body naturally responds when medication is withdrawn. Studies show that after GLP-1 and GIP-based weight loss injections are stopped, many people regain some weight, though often not all of the weight they lost. The amount regained depends on several factors: whether lifestyle changes (diet and exercise) have been maintained, your genetics, other medications you take, and any underlying metabolic conditions.
- Appetite regulation: Without the medication, hunger hormones (like ghrelin) increase naturally
- Metabolic adaptation: Your body may adapt to lower weight and resist further loss
- Lifestyle factors: If dietary and exercise habits revert to pre-treatment patterns, weight regain is more likely
- Dose reduction: Lowering your dose (rather than stopping completely) may reduce regain but may not prevent it entirely
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.
Managing Weight After Mounjaro — Practical Steps
If you're gaining weight after Mounjaro, speak to your GP or prescriber before making any changes. Weight regain can sometimes be managed by continuing treatment, adjusting your dose, or switching to another prescription weight loss injection such as Wegovy (semaglutide). Some patients benefit from longer-term maintenance therapy rather than stopping treatment altogether.
The most important factor in preventing regain is sustaining the dietary and lifestyle changes you made while on Mounjaro. Use our free progress tracker to monitor your weight regularly and catch changes early. Our GLP-1 weight loss calculator can help you understand how different doses affect potential weight loss if you restart or adjust your treatment. Discuss with your GP whether continuing at a lower maintenance dose, or exploring other weight management options, suits your individual health needs.
- 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 gaining weight after Mounjaro normal?
Yes, weight regain is common after stopping Mounjaro or reducing your dose. This is a natural response as your body's appetite regulation returns to baseline. However, the amount regained varies — many people do not regain all the weight they lost, especially if they maintain dietary and exercise changes made during treatment.
Can I prevent weight gain after stopping Mounjaro?
The best approach is to maintain the dietary and lifestyle habits you developed while on Mounjaro. Continuing some form of physical activity, eating mindfully, and staying in a modest calorie balance helps limit regain. Speak to your GP about whether continuing treatment at a lower dose might suit your needs.
Should I restart Mounjaro if I'm gaining weight back?
This is a decision to make with your prescriber or GP. Some people benefit from longer-term, ongoing treatment at a maintenance dose rather than stopping completely. Others may try dose reduction first. Your individual health, the reasons for stopping, and your weight management goals all factor into this decision.
What's the difference between Mounjaro and Wegovy for weight regain?
Both are prescription weight loss injections, but Mounjaro (tirzepatide) is a dual GIP and GLP-1 agonist, while Wegovy (semaglutide) is a GLP-1 agonist only. Clinical trials suggest Mounjaro may produce slightly larger average weight losses, though individual results vary. Your prescriber can advise which might suit you if switching is an option.
How long does it take to regain weight after stopping Mounjaro?
Weight regain typically begins within 1–2 weeks of stopping or reducing your dose, as appetite increases return. However, the pace and total amount regained varies greatly between individuals. Regular monitoring with our free weight converter and progress tracker helps you spot trends early and discuss options with your GP.
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.