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: Dose, Mechanism, and Trial Data
Mounjaro (tirzepatide) and Wegovy (semaglutide) are both prescription-only weight management injections available in the UK, but they work differently and have different maximum doses. Mounjaro reaches 15 mg once weekly, whilst Wegovy's maximum is 2.4 mg. The key difference is that Mounjaro is a dual GIP and GLP-1 receptor agonist, whereas Wegovy activates GLP-1 only. Both require clinical assessment before prescription. Understanding these differences helps you discuss options with your prescriber. Our GLP-1 weight loss calculator can help you explore potential outcomes at different doses.
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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.
How Mounjaro and Wegovy Differ: Mechanism and Dose Titration
Mechanism: Mounjaro works on two hormone pathways simultaneously — GIP (glucose-dependent insulinotropic polypeptide) and GLP-1 (glucagon-like peptide-1). This dual action may help regulate appetite, reduce food cravings, and support fuller feelings after meals. Wegovy activates only the GLP-1 pathway, which also reduces appetite but through a single mechanism.
Maximum doses: Mounjaro's maximum is 15 mg once weekly, titrated over approximately 20 weeks. Wegovy reaches 2.4 mg once weekly, titrated over approximately 16 weeks. The higher Mounjaro dose reflects its dual-action design.
Dose escalation: Both require a minimum of 4 weeks at each dose before increasing. Neither should be escalated faster than prescribed. Mounjaro's KwikPen contains 4 weeks of doses; Wegovy pens also contain 4 weeks supply.
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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.
SURMOUNT vs STEP: Clinical Trial Results Compared
Mounjaro's weight loss efficacy comes from the SURMOUNT-1 clinical trial, which showed average weight loss of approximately 15% at 5 mg, 19.5% at 10 mg, and 20.9% at 15 mg over 72 weeks. Wegovy's results come from the STEP-1 trial, showing approximately 14.9% average weight loss at the maximum 2.4 mg dose over 68 weeks. Both studies included participants alongside a reduced-calorie diet and increased physical activity. Individual results vary significantly. Both injections are available through NHS specialist weight management services or private prescription in the UK. Your GP or prescriber will assess which option suits your circumstances, medical history, and eligibility based on your BMI and health conditions.
- 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 does Mounjaro have a higher maximum dose than Wegovy?
Mounjaro's 15 mg maximum reflects its dual GIP and GLP-1 mechanism, which is more complex than Wegovy's single GLP-1 pathway. The higher dose is not "stronger" — it is simply how the medication is formulated. Both medications are effective; the choice depends on individual suitability and prescriber assessment.
Is Mounjaro more effective than Wegovy?
Clinical trials show Mounjaro achieved slightly higher average weight loss (up to 20.9%) compared to Wegovy (up to 14.9%), but differences are modest and individual results vary considerably. Neither medication assures weight loss. Prescriber assessment and personal factors determine which is more suitable for you.
How long does dose titration take for each medication?
Mounjaro takes approximately 20 weeks to reach maximum dose (15 mg), with 4-week intervals between increases. Wegovy takes approximately 16 weeks to reach maximum dose (2.4 mg), also with 4-week intervals. Faster titration is not recommended and may increase side effects.
Can I switch from Mounjaro to Wegovy or vice versa?
Yes, switching is possible but must be managed by your prescriber. There is no official established conversion chart between them — approximate equivalences exist but individual needs vary. Any medication switch requires clinical guidance and reassessment.
Which one is available on the NHS in the UK?
Both Mounjaro and Wegovy are available through NHS specialist tier 3 weight management services, though availability varies significantly by region and waiting lists can be lengthy. Both are also available privately through UK-licensed prescribers following online clinical assessment.
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.