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 — UK Cost and Effectiveness Comparison
If you're comparing Mounjaro and Wegovy as prescription weight loss options in the UK, cost is often a key factor — but mechanism and individual suitability matter equally. Both are prescription-only GLP-1 (or dual GIP/GLP-1) medications available through NHS specialist services or private online prescribing. This guide compares their mechanisms, clinical trial evidence, eligibility, and typical UK pricing to help you understand your options before speaking with a prescriber.
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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.
Clinical Evidence and Mechanism Differences
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, meaning it activates two hormone pathways simultaneously. In the SURMOUNT-1 clinical trial, participants achieved average weight loss of approximately 15% at 5mg, 19.5% at 10mg, and 20.9% at 15mg over 72 weeks alongside a reduced-calorie diet and increased physical activity. Individual results vary significantly.
Wegovy (semaglutide) is a single GLP-1 receptor agonist. In the STEP-1 trial, participants achieved average weight loss of approximately 14.9% at the maximum 2.4mg dose over 68 weeks under similar lifestyle conditions.
- Mounjaro's dual mechanism may offer slightly higher average weight loss in trials
- Both require weekly injections and dose titration over weeks
- Individual response is highly variable — some lose more on one than the other
- Neither assures specific weight loss outcomes
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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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UK Costs, Eligibility, and How to Access Each
Private prescribing costs (approximate UK range): Mounjaro typically £129–£320 per month depending on dose; Wegovy similarly £130–£300. Costs vary between online pharmacy providers. Both require an online clinical assessment (usually £20–£50) before prescription.
NHS access: Both are NICE-approved but access is through specialist tier 3/4 weight management services via GP referral. Eligibility requires BMI ≥30 or BMI 27–29.9 with weight-related health conditions (diabetes, hypertension, cardiovascular disease, sleep apnoea). Ethnicity-adjusted thresholds apply for South Asian, Black African, and Chinese adults. NHS waiting times vary dramatically by region — some areas have waits of 12–24 months. Your GP or a licensed prescriber can assess which is appropriate for you based on your individual health profile.
- 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.
Which is cheaper, Mounjaro or Wegovy, in the UK?
Costs are roughly comparable in private prescribing — typically £130–£320/month depending on dose and provider. Prices vary between online pharmacies, so it's worth comparing. NHS costs are the same for eligible patients, but availability varies by region. Always ask your prescriber or pharmacist for current pricing.
Does Mounjaro cause more side effects than Wegovy?
Both have similar common side effects: nausea, diarrhoea, constipation, stomach pain. The SURMOUNT and STEP trials showed comparable safety profiles. Individual tolerance varies — some people tolerate one better than the other. Your prescriber will monitor for any issues and can adjust your dose if needed.
Can I switch from Wegovy to Mounjaro or vice versa?
Yes, but any switch must be managed by your prescriber. There is no official conversion chart — your doctor will assess your current response and adjust accordingly. Switching typically involves a brief washout period and restarting titration on the new medication.
How long does each medication take to work?
Both medications work over time as you titrate doses. Most people notice appetite changes within the first few weeks, but significant weight loss typically takes 8–12 weeks to become apparent. Clinical trials measured results over 68–72 weeks. Be patient — medication works best alongside consistent diet and activity changes.
Do I need a prescription for Mounjaro or Wegovy in the UK?
Yes, both are prescription-only medicines. You cannot buy them over the counter. Access is through NHS specialist weight management services (via GP referral) or private online prescribing (following a clinical assessment by a UK-licensed prescriber). Always use a GPhC-registered pharmacy.
Ready to take control of your weight loss journey?
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