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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What's the Difference Between Mounjaro and Wegovy in the UK?
Mounjaro and Wegovy are both prescription-only weight management injections licensed in the UK, but they work differently and have different access routes and costs. Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, whilst Wegovy (semaglutide) is a GLP-1 agonist only. This guide explains how they differ in mechanism, dosing, expected results, and — crucially — how much they cost and where to access them in the UK through NHS or private prescription routes.
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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.
How Mounjaro and Wegovy Differ — And What This Means for Cost
Mechanism: Mounjaro works on two hormone pathways (GIP and GLP-1), whilst Wegovy targets one (GLP-1 only). This dual action in Mounjaro may explain why clinical trials showed slightly higher average weight loss — around 20.9% body weight at the maximum dose compared to Wegovy's approximately 14.9%. However, individual results vary considerably.
Dosing: Mounjaro starts at 2.5 mg and escalates to a maximum of 15 mg weekly over several months. Wegovy begins at 0.25 mg and reaches a maximum of 2.4 mg weekly. This means Mounjaro has more dose increments, allowing finer titration but also a longer escalation period.
Injection device: Mounjaro uses a KwikPen with 4 doses per pen (4 weeks supply). Wegovy uses a pre-filled auto-injection pen. Both are once-weekly injections. Cost per dose varies, but Mounjaro's longer titration means you spend more time on lower doses, which may affect overall cost trajectory during the first 4–6 months.
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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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NHS Access, Private Cost, and Where to Get Each in the UK
NHS access: Both Mounjaro and Wegovy are available through NHS tier 3 specialist weight management services following GP referral. However, availability is highly variable by region — some areas have long waiting lists (sometimes 12–24 months), whilst others have limited access. Ask your GP whether either is available in your ICB area.
Private prescription cost: Privately, Mounjaro typically costs £150–£300 per month depending on your current dose (lower doses cost less). Wegovy costs roughly £130–£250 per month. Private prescriptions are issued following an online clinical assessment with a UK-licensed prescriber through GPhC-registered pharmacies. Costs are per injection or per month, so budget accordingly for ongoing treatment. Use our free GLP-1 weight loss calculator to estimate potential outcomes and help decide which medication might suit 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 or Wegovy better for weight loss?
Clinical trials show Mounjaro achieved slightly higher average weight loss (20.9% body weight) than Wegovy (14.9%), but individual results vary significantly. "Better" depends on your health profile, side effect tolerance, and how your body responds. Your GP or prescriber will assess which is more suitable for you personally.
Can I switch from Wegovy to Mounjaro or vice versa?
Switching between medications must be managed by your prescriber. There is no official conversion chart, though approximate equivalences exist (e.g. Wegovy 1.7 mg ≈ Mounjaro 10 mg). Never switch without guidance — your prescriber will assess whether a switch is safe and will manage the transition.
How much does Mounjaro cost privately in the UK compared to Wegovy?
Private costs vary by provider and dose. Mounjaro typically ranges £150–£300/month; Wegovy ranges £130–£250/month. Lower doses cost less. Prices differ between online pharmacies, so compare before committing. NHS access (if available in your area) is free at point of care.
What's faster — NHS or private prescription for Mounjaro or Wegovy?
Private prescription is usually faster — typically 1–2 weeks from online assessment to first injection. NHS access depends on your local tier 3 waiting list, which can be months. If you need treatment urgently, private is faster; if cost is your priority, ask your GP about NHS availability.
Can my GP prescribe Mounjaro or Wegovy, or do I need a specialist?
In the UK, Mounjaro and Wegovy for weight management are typically initiated through NHS tier 3 specialist services, not routine GP practice. Privately, UK-licensed prescribers (often through online services) can prescribe following an assessment. Your GP can refer you to specialist services but cannot usually prescribe these medications directly.
Ready to take control of your weight loss journey?
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