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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Switching From 1mg Wegovy to Mounjaro in the UK
If you're taking 1mg Wegovy and wondering how this compares to Mounjaro, or whether switching might be right for you, this guide covers the approximate dose equivalence, how the two medications work differently, and what you need to know about accessing either medication through the NHS or privately in the UK. Both are prescription-only weight management injections, but they work in different ways and have different dosing schedules.
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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.
Understanding Dose Equivalence and Mechanisms
At 1mg Wegovy, you're on an escalation dose within the STEP clinical trial dosing schedule (0.25mg → 0.5mg → 1mg → 1.7mg → 2.4mg maximum). The approximate equivalent Mounjaro dose for 1mg Wegovy is around 5mg Mounjaro, though this is not an officially established conversion and individual responses vary.
The key difference: Wegovy (semaglutide) is a GLP-1 receptor agonist only, activating one hormone pathway. Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, activating two pathways simultaneously. This dual mechanism may explain why clinical trials showed Mounjaro produced slightly higher average weight loss (around 20.9% body weight at 15mg in SURMOUNT-1) compared to Wegovy (around 14.9% at 2.4mg in STEP-1), though individual results vary significantly.
Any switch between medications must be managed by your prescriber. You should never switch doses yourself—your GP or specialist will assess whether Mounjaro is appropriate for you and determine the starting dose.
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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
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NHS Access and Eligibility for Both Medications
Both Wegovy and Mounjaro are available through NHS specialist tier 3 weight management services, following NICE guidance. However, NHS access is limited and varies significantly by region and ICB (Integrated Care Board). Waiting lists can be several months to years in many areas.
To be eligible for either medication on the NHS, you must have a BMI of 30 or above, or 27–29.9 with weight-related health conditions (type 2 diabetes, hypertension, sleep apnoea, or cardiovascular disease). For South Asian, Black African, Black Caribbean, and Chinese adults, lower BMI thresholds apply.
For faster access, both medications are available privately through online prescribing services following a clinical assessment. Use the GLP-1 weight loss calculator on this page to explore potential outcomes, and speak with your GP about which route suits your 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.
Is 1mg Wegovy equivalent to 5mg Mounjaro?
Approximately, yes—1mg Wegovy is roughly equivalent to 5mg Mounjaro based on clinical trial data and prescribing practice. However, this is not an official conversion chart. Individual responses differ, and only a prescriber can assess whether you should switch and what dose is appropriate for you. Never switch without medical guidance.
Why is Mounjaro more effective than Wegovy if they're similar doses?
Mounjaro's dual GIP+GLP-1 mechanism is thought to produce greater appetite suppression and metabolic effects than Wegovy's GLP-1-only pathway. In trials, Mounjaro showed higher average weight loss. However, individual results vary—some people respond better to Wegovy, and some to Mounjaro. Your prescriber will choose based on your health profile.
Can I switch from Wegovy to Mounjaro on the NHS?
Potentially, yes, if you're receiving Wegovy through an NHS tier 3 weight management service. However, availability and switching protocols vary by region. You must request a review with your specialist team. Private access to Mounjaro may be faster, though it involves private prescription and pharmacy costs.
What are the side effects of Mounjaro compared to Wegovy?
Both cause similar common side effects: nausea, diarrhoea, vomiting, and constipation—especially during dose escalation. Individual tolerance varies. Most side effects diminish over weeks as your body adjusts. Serious side effects are rare but require immediate medical attention. Your prescriber will discuss these risks before starting either medication.
How long does it take to escalate from 1mg Wegovy to Mounjaro if I switch?
If switching to Mounjaro, your prescriber will likely start you at 2.5mg (the starting dose) rather than jumping to 5mg, to allow your body to adjust. Typically, you'll increase by 2.5mg every 4 weeks until reaching your target dose. The full escalation may take 12–20 weeks. Your prescriber will tailor this to your tolerance and response.
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