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 Eligibility in the UK
Both Mounjaro (tirzepatide) and Wegovy (semaglutide) are prescription weight loss injections available in the UK, but eligibility criteria are very similar. This guide explains who can access each medication, how they compare, and what to expect during clinical assessment. If you're considering a weight loss injection in the UK, understanding the eligibility requirements for both options will help you and your GP make an informed decision about which treatment might suit your needs best.
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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.
Eligibility Criteria for Mounjaro and Wegovy
Both Mounjaro and Wegovy share the same core UK eligibility requirements. You may be eligible if you have a BMI of 30 kg/m² or above, or a BMI of 27–29.9 kg/m² with at least one weight-related health condition. Weight-related conditions that qualify include type 2 diabetes or prediabetes, high blood pressure, abnormal blood fats, obstructive sleep apnoea, or a history of cardiovascular disease.
For adults of South Asian, Chinese, Black African, or Black Caribbean heritage, the NHS recommends lower BMI thresholds due to higher health risks at lower weights. In these groups, eligibility may start at BMI 27.5 or above without additional conditions.
Both medications are prescription-only and require a formal clinical assessment from a licensed prescriber. Neither can be obtained without a valid prescription. Age restrictions also apply — both are approved for adults only (18 years and over). Pregnancy, breastfeeding, or plans to become pregnant are contraindications for both Mounjaro and Wegovy.
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If your BMI suggests you're overweight or obese, explore our GLP-1 calculators to project potential weight loss on Mounjaro or Wegovy.
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How Mounjaro and Wegovy Compare: Mechanism and Dosing
The key difference lies in how they work. Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, meaning it activates two hormone pathways in your body. Wegovy (semaglutide) is a GLP-1 receptor agonist only, activating a single pathway. Clinical trial data from SURMOUNT (Mounjaro) showed average weight loss of approximately 15–21% of body weight, whilst STEP trials (Wegovy) showed around 15% average loss — though individual results vary significantly.
Dosing schedules differ slightly: Mounjaro starts at 2.5 mg and escalates to a maximum of 15 mg once weekly, whilst Wegovy starts at 0.25 mg and escalates to a maximum of 2.4 mg once weekly. Both are injected once weekly using a pre-filled pen. The choice between them depends on your individual health profile, how you respond to treatment, and what your prescriber recommends following your clinical assessment. Try our free GLP-1 weight loss calculator to explore potential outcomes with either medication, and use the BMI calculator to check your current status against eligibility thresholds.
- 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 minimum BMI to get Mounjaro or Wegovy on the NHS in the UK?
For most UK adults, the minimum BMI for NHS eligibility is 30 kg/m² without additional conditions, or 27–29.9 kg/m² with weight-related health conditions such as type 2 diabetes, high blood pressure, or cardiovascular disease. For South Asian, Chinese, Black African, or Black Caribbean adults, the threshold starts at BMI 27.5 kg/m² due to higher documented health risks at lower weights.
Can I get Mounjaro and Wegovy on the NHS, or only privately in the UK?
Both medications are available through NHS specialist tier 3 weight management services — this is the primary NHS route. However, NHS access varies significantly by region, and waiting lists can be lengthy. Both are also available through private online prescribing services following a clinical assessment with a UK-licensed prescriber. Private access typically does not require an NHS referral or lengthy waiting times.
Is Mounjaro better than Wegovy for weight loss?
Clinical trials showed Mounjaro achieved slightly higher average weight loss (15–21%) compared to Wegovy (around 15%), but individual results vary considerably. Both are effective weight loss injections. The choice between them depends on your personal health circumstances, how you respond to treatment, and what your prescriber recommends. Neither is universally "better" — suitability is individual.
Do I need a prescription from my GP to get Mounjaro or Wegovy?
Yes, both are prescription-only medicines in the UK. You cannot obtain either without a valid prescription. For NHS access, your GP will refer you to specialist services. For private prescribing, a UK-licensed prescriber will assess you online and issue a prescription if appropriate. The prescription is then dispensed by a GPhC-registered pharmacy.
What conditions make me ineligible for Mounjaro or Wegovy?
You cannot take either medication if you are under 18, pregnant, planning pregnancy, or breastfeeding. A personal or family history of medullary thyroid carcinoma, or multiple endocrine neoplasia type 2, are also contraindications. Severe stomach or digestion problems may also affect eligibility. Your prescriber will assess your full medical history during clinical assessment to confirm suitability.
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