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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Wegovy Injection in the UK — How It Compares to Mounjaro
Wegovy is a prescription-only weekly weight loss injection licensed in the UK for adults with obesity or excess weight. It works differently from Mounjaro, another popular weekly weight loss injection. Both are available through NHS specialist services or private prescribing, but they use different mechanisms and have different dose ranges. Understanding how they compare can help you and your GP or prescriber decide which might be right for your individual health needs. This guide breaks down the key differences in mechanism, trial results, dosing, and eligibility.
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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 Wegovy and Mounjaro Work — Mechanism and Trial Data
Wegovy (semaglutide) is a GLP-1 receptor agonist — it activates one natural hormone pathway in the gut. Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist — it activates two hormone pathways simultaneously. This dual action in Mounjaro may explain why some clinical trials showed slightly higher average weight loss compared to Wegovy, though individual results vary significantly.
In the STEP-1 clinical trial, Wegovy at its maximum dose (2.4 mg) helped participants lose an average of approximately 14.9% of their body weight over 68 weeks, alongside a reduced-calorie diet and increased physical activity. In the SURMOUNT-1 trial, Mounjaro at its maximum dose (15 mg) showed average weight loss of approximately 20.9% of body weight. However, these are trial averages — your personal results depend on many factors including your starting weight, genetics, lifestyle changes, and how your body responds to the medication.
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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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Dosing, Side Effects, and Individual Suitability
Wegovy doses range from 0.25 mg to a maximum of 2.4 mg, increased gradually over 16+ weeks. Mounjaro doses range from 2.5 mg to 15 mg, also increased gradually. Both are once-weekly injections. Side effects are similar between the two — nausea, diarrhoea, constipation, and stomach pain are common, especially at the start of treatment or after dose increases. Choosing between them is not about one being "better" — it depends on your individual health profile, medical history, and how your prescriber assesses your suitability. Your GP or a licensed prescriber will evaluate which medication is appropriate for you following a clinical assessment. Use our free GLP-1 weight loss calculator to explore potential outcomes at different doses, and our BMI calculator to see where you sit on NHS guidelines.
- 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 Wegovy or Mounjaro available on the NHS in the UK?
Both are NICE-approved for NHS specialist weight management services, but availability varies significantly by region and waiting times can be lengthy. Access is typically through tier 3 specialist services, not standard GP prescription. Private access is available through GPhC-registered online pharmacies following clinical assessment.
What's the main difference between Wegovy and Mounjaro?
Wegovy is a GLP-1 agonist (single hormone pathway). Mounjaro is a dual GIP and GLP-1 agonist (two pathways). This may contribute to slightly different weight loss profiles, but both require lifestyle changes alongside medication for best results.
Can I switch from Wegovy to Mounjaro or vice versa?
Yes, but only under prescriber guidance. There is no official conversion chart — approximate dose equivalences exist, but any switch must be managed by your prescriber to ensure safe transition.
What are the side effects of Wegovy in the UK?
Common side effects include nausea, diarrhoea, constipation, and stomach pain, especially when starting or increasing dose. These often reduce over time. Serious side effects are rare but require immediate medical attention (severe stomach pain, gallbladder problems, allergic reactions).
How do I know if I'm eligible for Wegovy or Mounjaro?
Both require a BMI of 30 or above, or 27–29.9 with a weight-related health condition (type 2 diabetes, high blood pressure, heart disease, sleep apnoea). A licensed prescriber will assess your individual health to determine suitability and which medication is appropriate for you.
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.