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: UK Eligibility and Access Routes
Both Mounjaro (tirzepatide) and Wegovy (semaglutide) are prescription-only weight management injections licensed in the UK, but they work differently and have distinct NHS and private access routes. This guide compares the two medications across mechanism, dosing, expected weight loss, and how to access them through the NHS or private services. Understanding the differences can help you discuss options with your GP or prescriber.
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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 Differ: Mechanism and Dosing
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist—it activates two hormone pathways, which is why it's structurally different from Wegovy. Wegovy (semaglutide) is a GLP-1-only receptor agonist. This dual mechanism may explain why Mounjaro users showed slightly higher average weight loss in clinical trials (approximately 20.9% body weight at maximum dose) compared to Wegovy users (approximately 14.9% body weight). However, individual results vary significantly.
Dosing differences: Mounjaro starts at 2.5 mg and escalates to a maximum of 15 mg once weekly. Wegovy starts at 0.25 mg and escalates to a maximum of 2.4 mg once weekly. Both are once-weekly injections administered via KwikPen. Mounjaro's KwikPen allows you to dial the dose, whilst Wegovy uses pre-filled pens for each dose level. When considering these weight loss injection options, use our GLP-1 weight loss calculator to explore potential outcomes at different doses based on clinical trial data.
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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 Tier 3 Specialist Access
In the UK, both medications are accessible through NHS specialist tier 3 weight management services, though availability varies significantly by region and ICB (Integrated Care Board). NICE has approved both tirzepatide (Mounjaro) and semaglutide (Wegovy) for use within NHS weight management pathways. Eligibility typically requires a BMI of 30 kg/m² or above, or 27–29.9 kg/m² with weight-related health conditions such as type 2 diabetes, hypertension, or cardiovascular disease. South Asian, Chinese, Black African, and Black Caribbean adults may qualify at lower BMI thresholds due to higher health risks at comparable weights. NHS waiting lists for specialist services can be substantial in many areas—months or longer in some regions.
Private access: Both medications are available through GPhC-registered online pharmacies following a clinical assessment with a UK-licensed prescriber. Private routes bypass NHS waiting lists but involve direct costs (typically £129–£320 per month depending on dose). Your GP can advise whether specialist NHS referral is appropriate or whether private options suit your circumstances.
Check your BMI using our free BMI calculator to understand your baseline, then discuss NHS or private options with your GP or a licensed prescriber to determine which route and medication is most suitable for your 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.
Which medication causes more weight loss—Mounjaro or Wegovy?
In clinical trials, Mounjaro showed slightly higher average weight loss (approximately 20.9% body weight) compared to Wegovy (approximately 14.9% body weight) at maximum doses. However, individual results vary widely and depend on adherence, lifestyle changes, and personal metabolism. Both medications work best alongside a reduced-calorie diet and increased physical activity.
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 between Mounjaro and Wegovy doses. If you're on an NHS specialist service, discuss a potential switch with your tier 3 team. Private prescribers can also manage switches, though individual circumstances differ.
How long does it take to see weight loss results with these injections?
Weight loss typically begins within 2–4 weeks of starting either medication, though the most significant changes occur over 12–16 weeks as your dose increases. Both medications require dose escalation over several weeks (4 weeks minimum per dose level) before reaching maximum effectiveness.
Is Mounjaro or Wegovy available on the NHS where I live?
Availability depends on your local ICB (Integrated Care Board). Some areas have robust specialist weight management services; others have limited NHS access. Contact your GP to ask whether your region offers NHS access to these medications or whether private options are more practical for you.
What happens if I stop taking Mounjaro or Wegovy?
Weight loss effects typically reverse over weeks to months after stopping either medication. Studies show that weight regain can occur if lifestyle changes (diet and exercise) are not maintained. Long-term management typically involves ongoing medication use alongside sustained behaviour change, as directed by your prescriber.
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.