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 — Understanding the Differences
Both Mounjaro (tirzepatide) and Wegovy (semaglutide) are prescription-only weight management injections available in the UK, but they work differently and have different dose schedules. Understanding the key differences between these medications can help you and your GP make an informed decision about which might be suitable for you. This guide compares the two side-by-side, focusing on mechanism, dose ranges, clinical trial results, and how to access each in the UK.
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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 Differently
The most important difference between these two medications lies in how they work:
- Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist — it activates two separate hormone pathways to help regulate appetite and blood sugar. GIP (glucose-dependent insulinotropic polypeptide) is an additional hormone that supports appetite control and fat utilisation.
- Wegovy (semaglutide) is a GLP-1 receptor agonist only — it activates a single hormone pathway. Both medications slow how quickly food leaves the stomach and signal fullness to the brain, but Mounjaro's dual mechanism is a key distinction.
Because of this difference, clinical trials showed Mounjaro achieved slightly higher average weight loss (around 15–21% of body weight) compared to Wegovy (around 14.9%), though individual results vary significantly. Neither medication is assured to produce these outcomes — your response depends on your metabolism, lifestyle, and consistency with diet and exercise changes.
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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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Dose Schedules and Eligibility in the UK
Mounjaro doses: Start at 2.5 mg weekly, escalate every 4 weeks (5 mg, 7.5 mg, 10 mg, 12.5 mg) up to a maximum of 15 mg once weekly. Wegovy doses: Start at 0.25 mg weekly, escalate over weeks (0.5 mg, 1 mg, 1.7 mg) up to a maximum of 2.4 mg once weekly.
Both are available to UK adults with a BMI of 30 kg/m² or above, or 27–29.9 kg/m² with weight-related health conditions (type 2 diabetes, high blood pressure, or cardiovascular disease). Access through NHS specialist weight management services involves a referral from your GP and can have significant waiting lists in many regions. Private access is available through GPhC-registered online pharmacies following a clinical assessment. Your prescriber will determine which medication, if any, is 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.
What is the main difference between Mounjaro and Wegovy?
Mounjaro is a dual GIP and GLP-1 receptor agonist, activating two hormone pathways. Wegovy is a GLP-1 receptor agonist only, activating one pathway. Both reduce appetite and slow digestion, but Mounjaro's dual mechanism may produce slightly higher average weight loss in clinical trials, though individual results vary.
What are the maximum doses for each medication?
Mounjaro's maximum dose is 15 mg once weekly. Wegovy's maximum dose is 2.4 mg once weekly. Both require gradual dose escalation over weeks or months, and your prescriber will determine the appropriate dose for you based on tolerability and effectiveness.
Which medication should I choose?
The choice between Mounjaro and Wegovy is made by your prescriber based on your health history, BMI, weight-related conditions, and individual factors. Neither is universally "better" — both are effective for many people. Your GP or specialist will discuss which is most suitable for you.
How do I access Mounjaro or Wegovy in the UK?
NHS access is through specialist tier 3 weight management services via GP referral, though waiting times vary significantly by region. Private access is available through online prescribing services. Both routes require a clinical assessment to confirm eligibility and suitability.
Can I switch from Mounjaro to Wegovy or vice versa?
Switching between medications is possible but must be managed by your prescriber. There is no established official conversion chart, though rough equivalences exist (e.g., Mounjaro 10 mg ≈ Wegovy 1.7 mg). Your prescriber will advise on timing and safety of any switch.
Ready to take control of your weight loss journey?
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