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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Wegovy Dose Compared to Mounjaro — What's the Difference?
Wegovy and Mounjaro are both prescription-only weight loss injections available in the UK, but they work differently and use different dose schedules. Wegovy (semaglutide) is a GLP-1 receptor agonist, whilst Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist — meaning Mounjaro activates two hormone pathways rather than one. Both are licensed for weight management in UK adults with a BMI of 30 or above, or 27 and above with weight-related health conditions. This guide explains the dose schedules, how they compare, and what the clinical evidence shows about effectiveness.
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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.
Wegovy vs Mounjaro: Dose Schedules and Starting Points
Wegovy (semaglutide) starts at a much lower dose than Mounjaro and titrates more gradually over 16 weeks:
- Weeks 1–4: 0.25 mg once weekly
- Weeks 5–8: 0.5 mg once weekly
- Weeks 9–12: 1 mg once weekly
- Weeks 13–16: 1.7 mg once weekly
- Week 17+: 2.4 mg once weekly (maximum maintenance dose)
Mounjaro (tirzepatide) also titrates weekly but reaches higher absolute doses:
- Weeks 1–4: 2.5 mg once weekly
- Weeks 5–8: 5 mg once weekly
- Weeks 9–12: 7.5 mg once weekly
- Weeks 13–16: 10 mg once weekly
- Weeks 17–20: 12.5 mg once weekly
- Week 21+: 15 mg once weekly (maximum dose)
The key difference is that Mounjaro's doses are expressed in absolute mg amounts, whilst Wegovy's maximum is 2.4 mg — but this does not mean Wegovy is "lower strength". The medications work through different mechanisms, so direct dose comparison is not straightforward.
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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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Clinical Results: Weight Loss Outcomes in Trials
Clinical trials show both medications support significant weight loss when used alongside reduced-calorie diet and increased physical activity. In the STEP-1 trial, Wegovy at 2.4 mg helped participants lose an average of approximately 14.9% of their body weight over 68 weeks. In the SURMOUNT-1 trial, Mounjaro at 15 mg helped participants lose an average of approximately 20.9% of their body weight over 72 weeks. However, individual results vary considerably — some people lose more, some less. Both medications are prescription-only and require a clinical assessment to determine suitability. Your GP or a licensed prescriber can discuss which option may be appropriate based on your personal health circumstances.
- 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.
Why do Mounjaro doses go higher than Wegovy if they're the same type of injection?
Mounjaro and Wegovy are not the same type of medication. Mounjaro is a dual GIP and GLP-1 agonist (activating two hormone pathways), whilst Wegovy is a GLP-1 agonist only (one pathway). This difference in mechanism means the dose schedules and maximum doses are different. Higher Mounjaro doses do not mean "stronger" — they reflect the different way the medication works in the body.
Can I switch from Wegovy to Mounjaro or vice versa?
Switching between these medications is possible but must be managed by your prescriber. There is no official established conversion chart between Wegovy and Mounjaro doses — approximate equivalences exist based on clinical practice, but any switch requires medical supervision. Your prescriber will assess whether a switch is appropriate and manage the transition carefully.
Which weight loss injection is more effective — Wegovy or Mounjaro?
Clinical trials suggest Mounjaro may result in slightly higher average weight loss than Wegovy, but individual results vary significantly. The SURMOUNT trial showed Mounjaro at maximum dose achieved ~clinically studied weight loss on average, whilst STEP trials showed Wegovy achieved ~15% on average. However, the "best" medication depends on your individual health, tolerability, and what your prescriber recommends after assessment.
How long does it take to reach the maximum dose of each medication?
Wegovy reaches maximum dose (2.4 mg) in 16 weeks. Mounjaro reaches maximum dose (15 mg) in 20 weeks. Both require a minimum of 4 weeks on each dose before escalation. After reaching maximum dose, you continue on that maintenance dose as long as the medication is working and you tolerate it well.
Are Wegovy and Mounjaro available through the NHS in the UK?
Both are licensed in the UK and can be accessed through NHS specialist tier 3 weight management services, though availability varies significantly by region and there can be substantial waiting lists. Both are also available privately through UK-licensed prescribers via online consultation, followed by dispensing through a GPhC-registered pharmacy. Access and costs differ between NHS and private routes.
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