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 vs Wegovy: Treatment Plan Comparison
If you're considering prescription weight loss treatment in the UK, you've likely heard about both Mounjaro (tirzepatide) and Wegovy (semaglutide). While both are once-weekly injections licensed for weight management, they work differently and follow distinct treatment plans. Understanding the differences—including how doses escalate, clinical trial results, and which might suit your individual circumstances—can help you have an informed conversation with your prescriber. Both require a clinical assessment before prescription, and individual suitability depends on your health profile and medical history.
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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 and Wegovy Treatment Plans Differ
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist—meaning it activates two natural hormone pathways simultaneously. This dual mechanism may help regulate appetite more effectively for some patients. The Mounjaro treatment plan starts at 2.5 mg once weekly for weeks 1–4, then escalates every 4 weeks through 5 mg, 7.5 mg, 10 mg, 12.5 mg, and up to a maximum of 15 mg. Clinical trial data from SURMOUNT-1 showed participants lost an average of 20.9% of their body weight on the 15 mg dose over 72 weeks, alongside a reduced-calorie diet and increased physical activity.
Wegovy (semaglutide) is a GLP-1-only receptor agonist—activating a single hormone pathway. The Wegovy treatment plan begins at 0.25 mg weekly and escalates through 0.5 mg, 1 mg, and 1.7 mg before reaching the maintenance dose of 2.4 mg. Clinical trial data from STEP-1 showed average weight loss of approximately 14.9% of body weight at 68 weeks on the maximum dose, also with lifestyle changes. The starting dose and escalation timescale differ significantly from Mounjaro.
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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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Which Treatment Plan Suits You: Prescriber Assessment
Both Mounjaro and Wegovy require a clinical assessment before prescription—your GP or prescriber will evaluate your individual health profile, medical history, and weight management goals. Eligibility in the UK applies to adults with a BMI of 30 or above, or 27 or above with weight-related health conditions such as type 2 diabetes, hypertension, or sleep apnoea. There is no universally "better" choice between them; suitability depends on your individual circumstances. Some prescribers may have more experience with one medication, while others may assess that the dual mechanism of Mounjaro suits your needs better than the single GLP-1 pathway. Use our free BMI calculator to check your current BMI category, and our GLP-1 weight loss calculator can help you understand projected outcomes at different dose levels for either medication.
- 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 key difference between Mounjaro and Wegovy?
Mounjaro is a dual GIP and GLP-1 receptor agonist (two hormone pathways), while Wegovy is a GLP-1-only agonist (one pathway). Mounjaro starts at 2.5 mg with a maximum of 15 mg. Wegovy starts at 0.25 mg with a maximum of 2.4 mg. Both are once-weekly injections licensed for weight management in the UK.
Which causes more weight loss—Mounjaro or Wegovy?
Clinical trials showed Mounjaro users lost an average of approximately 20.9% of body weight (at 15 mg), while Wegovy users lost approximately 14.9% (at 2.4 mg). However, individual results vary significantly, and a prescriber's choice depends on your personal health profile, not trial averages alone.
How long is a typical Mounjaro or Wegovy treatment plan?
Both medications are typically prescribed as ongoing treatment. Mounjaro takes approximately 16–20 weeks to reach maximum dose with 4-week intervals between escalations. Wegovy takes approximately 16 weeks to reach 2.4 mg. Treatment duration depends on your prescriber's guidance and your response.
Can I switch from Wegovy to Mounjaro or vice versa?
Any switch between medications must be managed by your prescriber. There is no official conversion chart—approximate equivalences exist (e.g., Wegovy 1.7 mg is roughly equivalent to Mounjaro 10 mg), but switching requires individual clinical assessment and prescription guidance.
How do I access a Mounjaro or Wegovy treatment plan in the UK?
NHS access is through specialist tier 3 weight management services (referral from your GP), though availability and waiting times vary by region. Private access is available through GPhC-registered online pharmacies following an online clinical assessment with a UK-licensed prescriber.
Ready to take control of your weight loss journey?
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