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 Dosage Chart vs Wegovy: UK Comparison
If you're considering prescription weight loss treatment in the UK, you may have heard about both Mounjaro and Wegovy. While both are once-weekly injections licensed for weight management, they work differently and have different dosage schedules. This guide compares the two medicines side-by-side so you understand how they differ. Remember, a prescriber will assess which is suitable for your individual health needs following a clinical assessment.
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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.
Dosage Schedules: Mounjaro vs Wegovy Comparison
Mounjaro (tirzepatide) uses a gradual four-week escalation pattern from 2.5 mg up to a maximum of 15 mg once weekly. The standard titration schedule is: 2.5 mg for weeks 1–4, then 5 mg for weeks 5–8, 7.5 mg for weeks 9–12, 10 mg for weeks 13–16, 12.5 mg for weeks 17–20, and finally 15 mg from week 21 onwards. Each KwikPen contains four weekly doses.
Wegovy (semaglutide) follows a longer escalation over approximately 16–20 weeks, starting at 0.25 mg and increasing through 0.5 mg, 1 mg, and 1.7 mg before reaching the maximum maintenance dose of 2.4 mg once weekly. The key difference is that Mounjaro's doses are significantly higher numerically because tirzepatide is a dual GIP and GLP-1 receptor agonist, whereas Wegovy is a GLP-1-only medication. These are not directly equivalent doses—the mechanisms and potency are different, so comparing the numbers directly can be misleading.
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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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Clinical Trial Results and Individual Variation
In the SURMOUNT-1 clinical trial, Mounjaro at the maximum 15 mg dose produced an average weight loss of approximately 20.9% of body weight over 72 weeks alongside reduced-calorie diet and increased physical activity. The STEP-1 trial for Wegovy showed average weight loss of around 14.9% body weight at the 2.4 mg dose over 68 weeks under similar lifestyle conditions. However, these are trial averages—individual results vary significantly, and some people lose more weight while others lose less. Your GP or prescriber will help determine which medication aligns with your health profile, as both require a clinical assessment before prescription. Use our GLP-1 weight loss calculator to explore projected outcomes at different doses.
- 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 is the starting dose for Mounjaro in the UK?
Mounjaro starts at 2.5 mg once weekly for the first four weeks. This allows your body to adjust to the medication. You remain on this dose for weeks 1–4, then escalate to 5 mg for weeks 5–8, and continue increasing every four weeks if tolerated. A prescriber will manage your dose escalation based on your individual response and side effects.
How does Mounjaro's mechanism differ from Wegovy?
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, meaning it activates two hormone pathways simultaneously. Wegovy (semaglutide) is a GLP-1-only agonist. The dual action in Mounjaro may contribute to its slightly higher average weight loss in clinical trials, but individual suitability varies. A prescriber will assess which suits your health needs.
Can I switch between Mounjaro and Wegovy in the UK?
Switching between these medications is possible but must be managed by your prescriber. There is no official conversion chart because they work via different mechanisms and have different potency. Any switch requires clinical assessment and dose adjustment. Never switch medications without guidance from your GP or the prescriber managing your treatment.
Which medication causes fewer side effects—Mounjaro or Wegovy?
Both medications have similar common side effects including nausea, diarrhoea, constipation, and stomach pain, particularly during dose escalation. Individual tolerance varies significantly. Some people tolerate one better than the other, but this is unpredictable and personal. Your prescriber will monitor your experience and adjust your dose or medication if needed.
How do I access Mounjaro or Wegovy on the NHS in the UK?
Both are available through NHS specialist tier 3 weight management services, but access varies significantly by region and waiting lists can be lengthy. Private prescription is available through UK-licensed online prescribers following a clinical assessment. Your GP can advise on NHS options in your area, or you can explore private prescribing directly through GPhC-registered pharmacies.
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