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
Free tracker included with every download this week
Mounjaro vs Wegovy — Comparing UK Weight Loss Options
When considering prescription weight loss treatment in the UK, you may wonder whether Mounjaro or Wegovy is right for you. Both are licensed GLP-1-based injections available through NHS specialist services or private online prescribing, but they work differently and produce different results. This guide compares the two medicines factually, helping you understand the key differences so you can have an informed conversation with your prescriber.
10,000+ calculations today · NHS-aligned thresholds · 100% free
Calculate Your BMI Instantly
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 Work Differently
Mounjaro (tirzepatide) is a dual mechanism medication — it activates both GIP and GLP-1 receptor pathways. This dual action may help regulate appetite, reduce food cravings, and support feeling fuller after meals. Wegovy (semaglutide) activates GLP-1 receptors only, producing a single-mechanism effect on appetite and gastric emptying.
Clinical trial data shows these differences translate to different weight loss outcomes. In the SURMOUNT-1 trial, Mounjaro at its maximum 15 mg dose achieved average weight loss of approximately 20.9% of body weight at 72 weeks. Wegovy, tested in the STEP-1 trial, achieved average weight loss of approximately 14.9% at 68 weeks on its maximum 2.4 mg dose. However, individual results vary significantly — your own response depends on your metabolism, lifestyle, and adherence to diet and exercise changes alongside the medication.
Clinically BackedWeight Loss
No appointments. No waiting rooms. Just care — from a UK-regulated online pharmacy.
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.
Free Weight Loss Tools & Guides
Everything you need to understand your weight, explore medication options, and track your progress — completely free.
Dosing, Eligibility, and Finding the Right Option for You
Mounjaro uses a faster dose titration schedule, reaching its maximum 15 mg dose by week 21. Wegovy escalates more gradually, reaching 2.4 mg by week 17. Both require a minimum of 4 weeks between dose increases. For UK eligibility, both medications are available to adults with a BMI of 30 or above, or 27–29.9 with weight-related health conditions such as type 2 diabetes, high blood pressure, or cardiovascular disease. South Asian, Chinese, Black African, and Black Caribbean adults may qualify at lower BMI thresholds due to higher health risk at lower weights. Your prescriber will assess you individually — there is no single "better" option. A clinical assessment determines which suits your health profile, preferences, and medical history. Both require a prescription and cannot be obtained without clinical evaluation.
- 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's the main difference between Mounjaro and Wegovy?
Mounjaro is a dual GIP and GLP-1 receptor agonist, activating two hormone pathways. Wegovy is a GLP-1-only medication. This dual mechanism in Mounjaro may explain its slightly higher average weight loss in clinical trials (20.9% vs 14.9%), though individual results vary considerably.
Can I switch from Wegovy to Mounjaro, or vice versa?
Yes, switching is possible, but it must be managed by your prescriber. There is no official conversion chart between the two. Your prescriber will assess whether a switch is appropriate for you and will guide your dosing if you do switch. Never change medications without medical guidance.
Which one is available on the NHS?
Both Mounjaro and Wegovy are approved by NICE for use within NHS specialist weight management services. However, NHS availability varies significantly by region, and waiting lists can be lengthy. Private prescribing through online services is faster but involves a cost, typically £129–£320 per month depending on dose.
Do both require a clinical questionnaire?
Yes. Both Mounjaro and Wegovy require a clinical assessment by a UK-licensed prescriber before a prescription is issued. This assessment includes a questionnaire about your medical history, current medications, allergies, and weight-related health conditions to ensure the medication is safe for you.
What if I have side effects on one — will the other be better?
Side effect profiles are similar between the two (nausea, diarrhoea, constipation, stomach pain are common with both). If you experience troublesome side effects, your prescriber may adjust your dose or suggest lifestyle changes before switching medications. Some people tolerate one better than the other, but this varies individually.
Ready to take control of your weight loss journey?
Start with a free BMI check, explore your GLP-1 options, or begin tracking your progress today. No sign-up. No cost. Just results.