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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Restarting Mounjaro or Wegovy: Which Is Right for You?
If you've paused or stopped weight loss treatment and are considering restarting, you may be wondering whether to go back to Mounjaro, switch to Wegovy, or try something different. Both are prescription-only GLP-1 receptor agonist medications licensed in the UK for weight management, but they work slightly differently and have different dose titration schedules. This guide compares both options factually so you can discuss your choice with your GP or prescriber.
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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.
Mounjaro vs Wegovy: Mechanism and Trial Data
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, meaning it activates two natural hormone pathways simultaneously. In the SURMOUNT-1 clinical trial, participants taking the maximum 15 mg dose lost an average of approximately 20.9% of their body weight over 72 weeks, alongside a reduced-calorie diet and increased physical activity.
Wegovy (semaglutide) is a GLP-1-only agonist. In the STEP-1 clinical trial, participants taking the maximum 2.4 mg dose lost an average of approximately 14.9% of their body weight over 68 weeks, also with dietary and lifestyle changes. Key differences include: Mounjaro starts at 2.5 mg weekly and escalates to 15 mg; Wegovy starts at 0.25 mg and escalates to 2.4 mg. Both require a minimum of 4 weeks on each dose before increasing.
- Average weight loss varies between individuals — clinical trial averages do not assures personal outcomes
- Both medications slow gastric emptying and reduce appetite signals
- Mounjaro's dual mechanism may offer slightly greater average weight loss, though individual results differ significantly
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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
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Restarting After a Break: Prescriber Assessment and Suitability
If you've stopped Mounjaro or Wegovy and want to restart, your prescriber will reassess your eligibility and health status. You'll need a new clinical evaluation — you cannot simply resume your previous dose without review. When restarting, most prescribers restart at the lowest dose (Mounjaro 2.5 mg or Wegovy 0.25 mg) and titrate up again, even if you previously tolerated higher doses.
The choice between restarting your original medication or switching depends on: why you stopped (side effects, cost, access), how you responded previously, current health status, and prescriber recommendation. Some people tolerate one medication better than the other. Use our free GLP-1 weight loss calculator to explore potential outcomes at different doses, and discuss both options with your GP to find what suits your situation best.
- 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.
Can I restart Mounjaro at the dose I was on before?
No. If you've had a break of more than a few weeks, most prescribers will restart you at the lowest dose (2.5 mg for Mounjaro) and titrate up gradually. Your prescriber will reassess your health before restarting. Never resume a higher dose without clinical guidance.
Is one medication better for restarting than the other?
Neither is universally "better" — it depends on your individual response. If you previously tolerated Mounjaro well, restarting it may be appropriate. If you experienced troublesome side effects, switching to Wegovy might be worth discussing. Your prescriber will assess which suits you best based on your history.
What happens if I've gained weight since stopping?
Weight regain after stopping is common and doesn't disqualify you from restarting. Your prescriber will reassess your BMI and eligibility. You'll need a new prescription and clinical assessment regardless of current weight.
How long does it take to reach my previous dose if restarting?
Mounjaro escalates weekly (4 weeks per dose level), so reaching 15 mg takes approximately 20 weeks. Wegovy escalates weekly too, reaching 2.4 mg in approximately 17 weeks. Your prescriber may adjust this timeline based on your tolerance and response.
Should I restart through the NHS or private prescriber?
Both routes require a clinical assessment. NHS access is through tier 3 specialist weight management services (variable waiting times by region). Private online prescribers offer faster access following an online assessment. Discuss availability and costs with your GP first.
Ready to take control of your weight loss journey?
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