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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Is Wegovy the Same as Mounjaro? NHS UK Differences Explained
No, Wegovy and Mounjaro are not the same medication, though both are prescription-only weight loss injections licensed in the UK. The key difference is how they work: Mounjaro uses a dual GIP and GLP-1 mechanism, while Wegovy is a GLP-1 agonist only. Both are approved for adults with a BMI of 30 or above, or 27 or above with weight-related health conditions, but they have different doses, injection schedules, and clinical trial results. Understanding these differences helps your GP or prescriber recommend the best option for your individual circumstances.
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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.
NHS Eligibility and How the Medications Differ
Mounjaro (tirzepatide) is manufactured by Eli Lilly and activates two hormone pathways: GIP (glucose-dependent insulinotropic polypeptide) and GLP-1. In the SURMOUNT-1 clinical trial, it helped participants lose an average of 15–21% of body weight at maximum dose (15 mg once weekly). The starting dose is 2.5 mg, escalating weekly to a maximum of 15 mg over several months.
Wegovy (semaglutide) is made by Novo Nordisk and activates GLP-1 only. Clinical trial data (STEP-1) showed an average weight loss of approximately 15% of body weight at the maximum dose of 2.4 mg once weekly. The starting dose is much lower at 0.25 mg, increasing gradually over 16 weeks.
Both require a prescription following clinical assessment and are administered as once-weekly injections. NHS access to either medication is through specialist tier 3 or tier 4 weight management services, and availability varies significantly by region. Your GP can refer you for specialist assessment, though waiting lists can be lengthy in many areas.
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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.
Free Weight Loss Tools & Guides
Everything you need to understand your weight, explore medication options, and track your progress — completely free.
NHS vs Private Access and Getting Started in the UK
Through the NHS, both medications are prescribed by specialist weight management services following a full health assessment. However, NHS availability and waiting times vary considerably depending on your local integrated care board (ICB). Some regions have established pathways; others have extended waiting lists.
Private online prescribing offers faster access without NHS referral — a UK-licensed prescriber assesses your eligibility via online consultation, and if suitable, your prescription is dispensed by a GPhC-registered pharmacy. Costs range from approximately £129–£320 per month depending on dose and provider. Use our free GLP-1 weight loss calculator above to estimate potential results at different doses, and calculate your BMI to confirm eligibility before exploring either route.
- 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 more effective — Wegovy or Mounjaro?
Clinical trials suggest Mounjaro may produce slightly higher average weight loss (15–21% vs 15%), but individual results vary significantly. Effectiveness depends on your personal response, adherence, diet, and activity level. Your prescriber will recommend the most suitable option based on your health profile.
Can I switch from Wegovy to Mounjaro on the NHS?
Switching between medications is possible but requires prescriber guidance. There is no official NHS conversion chart — any switch must be managed carefully by your specialist weight management service. The approximate Mounjaro equivalent to Wegovy 2.4 mg is 10 mg, but this is indicative only.
Are Wegovy and Ozempic the same thing?
Both contain semaglutide, but Ozempic is licensed for type 2 diabetes (doses up to 2 mg) and is not approved for weight loss in the UK. Wegovy is the licensed weight management version at 2.4 mg maximum. Never use Ozempic for weight loss — always use the correct licensed product under prescriber supervision.
What are the main side effects of both medications?
Both commonly cause nausea, diarrhoea, vomiting, and constipation, especially during dose escalation. Most side effects improve over time. Serious side effects are rare but include severe stomach pain (possible pancreatitis) and gallbladder problems. Always report new symptoms to your prescriber or GP immediately.
How long do I need to take Wegovy or Mounjaro?
These are ongoing treatments — most people continue as long as they remain beneficial and tolerated. Stopping either medication typically results in weight regain. Your GP or specialist will review your progress regularly and discuss whether to continue, adjust dose, or switch medications based on your response.
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.