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 — NHS UK Comparison Guide
Both Mounjaro (tirzepatide) and Wegovy (semaglutide) are prescription-only weight management injections licensed in the UK, but they work differently and have different NHS prescribing pathways. Understanding the differences—mechanism, dosing, eligibility criteria, and access routes—can help you discuss options with your GP or prescriber. This guide compares both medications in an NHS and UK context, covering NICE guidance, MHRA status, and eligibility thresholds across different regions.
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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 Work — Mechanism Differences
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, meaning it activates two natural hormone pathways simultaneously. This dual mechanism may help reduce appetite more effectively and support faster weight loss in clinical trials. Mounjaro uses a KwikPen device for once-weekly injection.
Wegovy (semaglutide) is a GLP-1 receptor agonist only, activating a single hormone pathway. It has been used in weight management longer and has extensive clinical trial data (STEP trials) supporting its safety and efficacy. Wegovy is also a once-weekly injection.
- Mounjaro: average 15–clinically studied weight loss in clinical trials (SURMOUNT-1)
- Wegovy: average clinically studied weight loss in clinical trials (STEP-1)
- Individual results vary significantly and depend on diet, activity, and adherence
- Both require a reduced-calorie diet and increased physical activity for best results
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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 Prescribing Pathways
In the UK, both Mounjaro and Wegovy are licensed for weight management through NHS specialist tier 3 services, though NICE approval varies by region and ICB (Integrated Care Board). Eligibility typically requires a BMI of 30 or above, or 27–29.9 with weight-related health conditions (type 2 diabetes, hypertension, cardiovascular disease, sleep apnoea). For adults of South Asian, Chinese, Black African, or Black Caribbean heritage, lower BMI thresholds (27.5+) may apply due to higher metabolic risk.
NHS access involves referral to a specialist weight management service—waiting lists vary from weeks to many months depending on your region. Private prescribing is available through UK-licensed online prescribers following clinical assessment, with no NHS referral needed. Use our GLP-1 weight loss calculator to explore potential outcomes, and our BMI calculator to check your starting point.
NHS prescribing of both medications is managed through tier 3 services, not standard GP prescription. Availability depends on your local ICB—some regions have better access than others. NICE guidance supports both as effective treatments alongside lifestyle changes. Both medications have MHRA approval with additional monitoring (Black Triangle ▼ status), meaning they're regularly reviewed for safety.
- Both require ongoing monitoring: blood glucose, kidney function, weight, and side effect management
- Private access is faster but costs approximately £129–£320/month depending on dose
- NHS access is free but involves waiting and specialist assessment
- A licensed prescriber will assess contraindications: pregnancy, pancreatitis history, gastroparesis, severe kidney/liver disease
- Switching between medications requires prescriber guidance—direct switching is not recommended
- 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.
Can the NHS prescribe Mounjaro and Wegovy in the same region?
Yes, both are NICE-approved for NHS specialist weight management services. However, availability varies significantly by ICB. Some regions may prioritise one over the other based on formulary decisions, cost, or demand. Your GP referral to tier 3 services will determine which medications your local service offers.
What's the key difference between Mounjaro's and Wegovy's mechanism?
Mounjaro is a dual GIP and GLP-1 agonist (two hormone pathways), while Wegovy is GLP-1 only (one pathway). This dual action may help Mounjaro deliver slightly higher average weight loss in trials, but individual responses vary. Neither is "better"—the right choice depends on your health profile and how you respond.
How long does it take to access these medications through the NHS?
Tier 3 weight management services typically have waiting lists ranging from 3 months to over a year depending on your region. Once referred, initial assessment takes 4–8 weeks, and dose titration adds another 12–16 weeks before reaching a maintenance dose. Private prescribing is available within days of consultation.
Are Mounjaro and Wegovy safe to switch between?
Switching between them is not straightforward. If you're on Mounjaro and want to try Wegovy (or vice versa), your prescriber must manage the transition carefully—there's no official conversion chart. Discuss switching options with your GP or prescriber, as it may involve a washout period.
What happens to weight after stopping Mounjaro or Wegovy?
Weight regain is common after stopping either medication if lifestyle changes aren't maintained. Clinical data shows that weight tends to return gradually if reduced-calorie diet and increased activity stop. This is why both medications are intended as long-term treatments alongside sustained lifestyle changes.
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.