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
Free tracker included with every download this week
Wegovy to Mounjaro Conversion Guide for UK Adults
Switching from Wegovy (semaglutide) to Mounjaro (tirzepatide) is a decision that requires GP or prescriber guidance — there is no official NHS conversion chart. Both are GLP-1 medications licensed for weight management in the UK, but they work slightly differently. Mounjaro uses a dual mechanism (GIP and GLP-1 activation), while Wegovy activates GLP-1 alone. This guide explains approximate dose equivalences, what to expect during a switch, and how to discuss this with your prescriber. Always consult your GP before changing any weight loss medication.
10,000+ calculations today · NHS-aligned thresholds · 100% free
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.
Approximate Dose Equivalence Between Wegovy and Mounjaro
While there is no official conversion formula, clinical practice suggests approximate equivalence between Wegovy (semaglutide) and Mounjaro (tirzepatide) doses based on their mechanisms and trial data:
- Wegovy 0.5 mg ≈ Mounjaro 5 mg — Both are starting escalation doses
- Wegovy 1.7 mg ≈ Mounjaro 10 mg — Mid-range maintenance doses
- Wegovy 2.4 mg ≈ Mounjaro 15 mg — Maximum licensed doses
These equivalences are approximate only and based on clinical experience, not official NHS guidance. The dual GIP+GLP-1 mechanism of Mounjaro may produce different effects than semaglutide's single GLP-1 activation, so individual response can vary significantly. Your prescriber will assess whether to start at an equivalent dose or restart at a lower dose for safety. Never adjust doses yourself — any switch requires professional medical oversight.
Clinically BackedWeight Loss
No appointments. No waiting rooms. Just care — from a UK-regulated online pharmacy.
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.
Key Differences: Why Dose Conversion Isn't Straightforward
Mounjaro and Wegovy are not identical medications, which is why direct conversion is complicated. Mounjaro activates both GIP and GLP-1 receptors (dual agonist), while Wegovy activates GLP-1 alone (single agonist). This dual action may produce a stronger appetite suppression effect, meaning you might need a lower Mounjaro dose than the Wegovy equivalent for similar results. Clinical trial data shows Mounjaro achieved slightly higher average weight loss (~20.9% at maximum dose) than Wegovy (~14.9%), but individual results vary significantly. Your prescriber may restart you at a lower dose when switching to allow your body to adjust to the different mechanism. Use our free GLP-1 weight loss calculator to estimate potential outcomes at different doses.
- 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.
Can I switch directly from Wegovy 2.4 mg to Mounjaro 15 mg?
Not recommended without professional assessment. Though approximate equivalence suggests 2.4 mg Wegovy ≈ 15 mg Mounjaro, your prescriber may restart you at a lower Mounjaro dose (e.g. 2.5 mg) due to the dual mechanism. Switching medications requires a clinical assessment by your GP or specialist to ensure safety and tolerability.
What happens if I miss a dose during the switch from Wegovy to Mounjaro?
If you miss a Wegovy dose within 4 days, take it as soon as remembered. If switching to Mounjaro, your prescriber will establish a new injection schedule — do not skip doses of either medication without guidance. Maintain your current medication until your prescriber confirms when to start the new one.
Is Mounjaro better than Wegovy for weight loss?
Clinical trials show Mounjaro produced slightly higher average weight loss (~21% vs ~15%), but individual results vary considerably. "Better" depends on your personal response, side effects, and health factors. Your prescriber will recommend the most suitable option based on your medical history and previous medication response.
Will my side effects change if I switch from Wegovy to Mounjaro?
Possibly. Both cause similar common side effects (nausea, diarrhoea, constipation), but the dual GIP+GLP-1 mechanism of Mounjaro may produce different tolerability. Some people report fewer gastrointestinal side effects with Mounjaro; others experience more. Your prescriber will monitor your tolerance during the transition.
Do I need an NHS referral to switch from Wegovy to Mounjaro?
If you're on Wegovy through NHS specialist services, your prescriber will manage any switch within those services. If using private Wegovy, switching to Mounjaro requires a new prescription from a UK-licensed prescriber following a fresh clinical assessment. Both medications are prescription-only in the UK.
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.