The UK's most complete GLP-1 guide
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- 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 — Understanding Equivalent Doses in the UK
Both Mounjaro (tirzepatide) and Wegovy (semaglutide) are prescription-only weight management injections available in the UK, but they work differently and are dosed differently. While approximate dose equivalents exist, these are clinical estimates only—any switch between medications must be managed by your prescriber. This guide explains how the two compare in UK context and what NHS access looks like for each.
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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 Differ — And What That Means for Dosing
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, whilst Wegovy (semaglutide) is a GLP-1 agonist only. This means Mounjaro activates two hormone pathways, potentially explaining why clinical trials showed a higher average weight loss (~20.9% at the maximum 15 mg dose) compared to Wegovy (~14.9% at 2.4 mg). Because of this different mechanism, doses are not directly interchangeable. The approximate equivalent doses are: Mounjaro 5 mg ≈ Wegovy 0.5 mg, Mounjaro 10 mg ≈ Wegovy 1.7 mg, and Mounjaro 15 mg ≈ Wegovy 2.4 mg. However, these are clinical estimates based on prescribing practice—not official conversion guidelines. Your prescriber will assess which medication suits your individual health needs. Both medications are injected once weekly using a pre-filled pen (Mounjaro's KwikPen or Wegovy's auto-injection pen). Side effects are similar between the two and commonly include nausea, diarrhoea, constipation, and stomach pain, though individual tolerance varies. Your GP or specialist can help you understand which option is appropriate for you based on your medical history and weight loss goals.
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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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NHS Eligibility and Access Routes for Both Medications
In the UK, both Mounjaro and Wegovy are available through NHS specialist tier 3 weight management services and through private online prescribing. NHS eligibility is the same for both: a BMI of 30 or above, or 27–29.9 with a weight-related health condition such as type 2 diabetes, prediabetes, high blood pressure, or sleep apnoea. For South Asian, Chinese, Black African, or Black Caribbean adults, lower thresholds may apply. NHS access varies significantly by region and can involve waiting lists. Private access is faster—available within days through GPhC-registered online pharmacies following a clinical assessment. Costs vary by dose and provider. Check your BMI using our free BMI calculator to see whether you might be eligible for either option, then discuss with your GP which route is most suitable for you.
- 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 Mounjaro more effective than Wegovy?
Clinical trials showed Mounjaro produced higher average weight loss (up to 20.9% body weight) than Wegovy (around 14.9%). However, individual results vary considerably. The dual mechanism of Mounjaro may account for this difference, but which is "better" depends on your personal response, side effect tolerance, and medical history. Your prescriber can advise which is more suitable for you.
Can I switch from Wegovy to Mounjaro on the NHS?
Possibly, but it depends on your local NHS tier 3 service and clinical circumstances. Any switch between medications must be managed by your prescriber—never switch on your own. Discuss this with your GP or specialist weight management clinic. Private prescribers may also facilitate a switch if clinically appropriate.
What's the maximum dose of each medication?
Mounjaro's maximum dose is 15 mg once weekly. Wegovy's maximum dose is 2.4 mg once weekly. Both are titrated (increased gradually) over weeks to reach the target dose. Starting doses are lower (Mounjaro 2.5 mg, Wegovy 0.25 mg) to allow your body to adjust and manage side effects.
Are Mounjaro and Wegovy available on the NHS in my area?
Availability varies significantly by region and NHS integrated care board (ICB). Some areas have well-established tier 3 weight management services offering both medications; others have limited access or waiting lists of months. Contact your GP to ask whether either medication is available through your local NHS services.
How do I know which medication is right for me?
Your GP or specialist prescriber will assess your medical history, current medications, previous weight loss efforts, and personal preferences. Both medications require a clinical assessment before prescription. Your prescriber will discuss the mechanism, likely side effects, dosing schedule, and expected outcomes for each option based on your individual circumstances.
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