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 Wegovy and Mounjaro?
Both Wegovy (semaglutide) and Mounjaro (tirzepatide) are prescription-only weight management injections licensed in the UK, but they work in different ways and have different eligibility criteria. Understanding the key differences can help you and your GP decide which might be suitable for you. Both require clinical assessment before prescription, and both are typically available through NHS specialist services or private prescribers. This guide explains how they compare in terms of mechanism, dosing, expected weight loss, and UK access 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 Wegovy and Mounjaro Differ — Mechanism and Dosing
Wegovy (semaglutide) is a GLP-1 receptor agonist — it activates a single natural hormone pathway in your gut to reduce appetite, increase fullness, and slow gastric emptying. The STEP clinical trials showed an average weight loss of approximately 14.9% of body weight at the maximum dose of 2.4 mg once weekly, taken alongside a reduced-calorie diet and physical activity.
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist — it activates two hormone pathways simultaneously, which is why it's considered a distinct advancement. The SURMOUNT-1 clinical trial demonstrated average weight loss of approximately 20.9% of body weight at the maximum 15 mg dose, also with lifestyle changes. Mounjaro uses a KwikPen device like Wegovy and is also a once-weekly injection, but the dosing schedule is different — it starts at 2.5 mg and escalates over 16–20 weeks to reach 15 mg.
- Wegovy: GLP-1 only, 0.25 mg to 2.4 mg (5 escalation steps)
- Mounjaro: GLP-1 + GIP dual action, 2.5 mg to 15 mg (6 escalation steps)
- Both: once-weekly injections, require 4 weeks minimum on each dose before escalating
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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 Eligibility and UK Access Routes
Both Wegovy and Mounjaro are available on the NHS through specialist tier 3 weight management services, though regional availability varies significantly. NHS eligibility is the same for both: adults with BMI 30 or above, or BMI 27–29.9 with weight-related health conditions such as type 2 diabetes, high blood pressure, or cardiovascular disease. Lower BMI thresholds apply for South Asian, Chinese, Black African, and Black Caribbean adults. NHS prescribing is typically managed through a GP referral to a specialist weight management service — waiting lists can be long in many areas.
Privately, both are accessible through online clinical assessments without NHS referral. Use our free BMI calculator above to check if you meet the eligibility criteria. Your GP or a licensed prescriber can advise which option is most appropriate for 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.
Is Mounjaro more effective than Wegovy?
Clinical trials show Mounjaro achieved higher average weight loss (20.9% vs 14.9%), but individual results vary significantly. Effectiveness depends on many factors including adherence, diet, activity level, and personal response. Both are evidence-based options — your GP will assess which suits you best based on your health profile.
Can I switch from Wegovy to Mounjaro on the NHS?
Yes, if medically appropriate. This would be managed through your specialist weight management service. Approximate equivalent doses exist (Wegovy 2.4 mg ≈ Mounjaro 15 mg), but any switch requires assessment and guidance from your prescriber.
Are the side effects the same for both?
Both share common side effects: nausea, diarrhoea, vomiting, and constipation, particularly in early weeks. Mounjaro may carry slightly different risk profiles due to its dual mechanism. Your prescriber will discuss side effects specific to each medication during your assessment.
How long do I need to stay on Wegovy or Mounjaro?
Both are typically recommended as longer-term treatments. Many people continue beyond initial weight loss to maintain results. Duration depends on individual response, weight management goals, and ongoing health assessment with your prescriber.
Does the NHS cover the cost of both medications?
Yes, both Wegovy and Mounjaro are available on the NHS through specialist services at no cost to eligible patients. Waiting lists vary by region. Privately, costs typically range from £120–£320 per month depending on dose and provider.
Ready to take control of your weight loss journey?
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