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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Mounjaro Maintenance vs Wegovy: Key Differences
Both Mounjaro (tirzepatide) and Wegovy (semaglutide) are prescription-only weight loss injections available in the UK, but they work differently and have different maintenance doses. Mounjaro uses a dual GIP and GLP-1 mechanism, while Wegovy is a GLP-1-only receptor agonist. Understanding the differences between their maintenance phases can help you and your prescriber discuss which option may be more suitable for your individual circumstances. This guide compares both medications factually, based on clinical trial data and UK prescribing guidelines.
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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.
Maintenance Doses and Trial Comparison
Mounjaro reaches its maintenance dose of 15 mg once weekly after a 20-week titration schedule, starting at 2.5 mg. Wegovy reaches 2.4 mg once weekly after a 16-week titration, starting at 0.25 mg. In the SURMOUNT-1 trial, Mounjaro at 15 mg produced average weight loss of approximately 20.9% of body weight over 72 weeks. In the STEP-1 trial, Wegovy at 2.4 mg produced average weight loss of approximately 14.9% over 68 weeks — both alongside reduced-calorie diet and increased physical activity. The key difference is mechanism: Mounjaro activates both GIP and GLP-1 pathways, while Wegovy activates GLP-1 only. This dual action in Mounjaro may explain slightly higher average weight loss in trials, though individual results vary significantly. Both medications slow stomach emptying and reduce appetite, but through different hormonal pathways.
- Mounjaro: 20-week titration to 15 mg maintenance
- Wegovy: 16-week titration to 2.4 mg maintenance
- Mounjaro trial: ~20.9% average weight loss at 15 mg
- Wegovy trial: ~14.9% average weight loss at 2.4 mg
- Both require ongoing weekly injections at maintenance dose
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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.
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Choosing Between Mounjaro and Wegovy Maintenance
Whether Mounjaro or Wegovy is more suitable depends on your individual health profile, and this decision should be made with a UK-licensed prescriber following a proper clinical assessment. Both medications require BMI of 30 or above, or 27–29.9 with weight-related health conditions (lower thresholds apply for South Asian, Chinese, Black African, and Black Caribbean adults). Your prescriber will consider your medical history, current medications, gastrointestinal function, and personal preferences. Some individuals respond better to one medication than the other — there is no universal "better" option. You can use our free GLP-1 weight loss calculator and BMI calculator to understand your starting point and estimated eligibility, but a prescriber must assess you individually before prescribing. Both are prescription-only and available through NHS specialist weight management services (with waiting lists varying by region) or private online prescribing following clinical assessment.
- 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's the difference between Mounjaro and Wegovy mechanisms?
Mounjaro (tirzepatide) activates both GIP and GLP-1 hormone pathways, creating a dual effect on appetite and blood sugar. Wegovy (semaglutide) activates GLP-1 only. This dual mechanism in Mounjaro may contribute to slightly higher average weight loss in clinical trials, though individual results vary. Both slow gastric emptying and signal fullness to the brain.
How long does it take to reach maintenance dose with each?
Mounjaro takes 20 weeks to reach the 15 mg maintenance dose, increasing by 2.5 mg every 4 weeks. Wegovy takes 16 weeks to reach 2.4 mg maintenance, increasing gradually from 0.25 mg. Both must remain on each dose for at least 4 weeks before escalating. Your prescriber may adjust the timeline based on your response and side effects.
Which produced better weight loss in clinical trials?
Mounjaro at 15 mg produced approximately 20.9% average weight loss in the SURMOUNT-1 trial, while Wegovy at 2.4 mg produced approximately 14.9% in the STEP-1 trial. However, clinical trial averages do not predict individual outcomes — some people lose more, some less. Results were achieved alongside reduced-calorie diet and exercise in both trials.
Can I switch from Wegovy to Mounjaro, or vice versa?
Switching between medications should only be done under prescriber guidance. Approximate dose equivalences exist (Wegovy 2.4 mg is roughly equivalent to Mounjaro 10–15 mg), but there is no official conversion chart. Your prescriber will assess whether switching is appropriate and manage any transition carefully to minimise side effects.
How do I know which medication is suitable for me?
Your prescriber will assess your eligibility (BMI and health conditions), medical history, medications you take, and any gastrointestinal issues. Both require prescription-only assessment. The NHS recommends specialist tier 3 weight management services for prescription access, though private online prescribing is also available in the UK. No medication is assured to work — individual suitability varies.
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