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 Wegovy To Mounjaro In The UK
Many UK adults using Wegovy (semaglutide) are considering switching to Mounjaro (tirzepatide) due to differences in mechanism, results, or side effects. Both are prescription-only GLP-1 and GLP-1/GIP receptor agonist medications licensed for weight management in the UK. Understanding the cost, eligibility, and access routes — whether through the NHS or privately — is essential before making any switch. This guide covers what you need to know about transitioning between these medications in a UK context.
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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.
Cost And Access: NHS Vs Private Routes
Accessing Mounjaro in the UK depends on your route: NHS or private prescription.
NHS access: Mounjaro is approved by NICE for use within specialist weight management services (tier 3 or 4). Availability and waiting times vary significantly by region and integrated care board (ICB). Some areas have good access; others have long waiting lists of several months or longer. You'll need referral from your GP to a specialist service. Once prescribed, the cost is covered by the NHS.
Private access: Available through GPhC-registered online prescribers following a clinical assessment. Private prescription costs for Mounjaro typically range from approximately £129 to £320 per month depending on your dose — the KwikPen contains 4 weeks' supply at a single dose. Starting at 2.5 mg and increasing through dose titration means early costs may be lower, rising as you progress to maintenance doses like 10 mg or 15 mg.
If you're currently on Wegovy privately, switching to Mounjaro involves a new clinical assessment with a prescriber, as the medications work differently and may require individualised dosing.
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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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What To Expect When Switching: Process And Timing
Switching from Wegovy to Mounjaro requires stopping Wegovy and starting Mounjaro on a structured schedule. Do not simply stop one and start the other — always follow your prescriber's guidance. Most commonly, you'll complete your final Wegovy dose, then begin Mounjaro at the starting dose (2.5 mg) after a gap of a few days. Since Mounjaro uses dose titration — increasing gradually over weeks — you may experience a different side effect profile than on Wegovy, even if you previously tolerated Wegovy well. Use our free GLP-1 weight loss calculator to understand potential outcomes at different Mounjaro doses, and track your progress during the transition with our free progress tracker to monitor how your body responds to the new medication.
- 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.
How much does Mounjaro cost privately in the UK?
Private Mounjaro costs typically range from £129 to £320 per month depending on your dose. A single KwikPen supplies 4 weeks at one dose level. Early doses (2.5 mg, 5 mg) are usually cheaper; higher maintenance doses (10–15 mg) are more expensive. Costs vary slightly between providers.
Can I switch from Wegovy to Mounjaro on the NHS?
Potentially yes, if you're under specialist weight management services. However, you'd need to discuss this with your specialist team, as switching between medications isn't automatic. NHS availability of Mounjaro varies by region — some areas have limited access. Your GP can advise on local availability.
What's the difference between Mounjaro and Wegovy that matters for switching?
Mounjaro is a dual GIP and GLP-1 receptor agonist; Wegovy is GLP-1 only. Mounjaro may work differently for you — some people achieve better results, others prefer Wegovy. Clinical trials showed Mounjaro produced slightly higher average weight loss, but individual results vary significantly. Your prescriber will assess which is better for your situation.
Do I need a new clinical assessment to switch to Mounjaro?
Yes. Mounjaro is a different medication with different eligibility criteria, dosing, and potential interactions. A prescriber will conduct a fresh assessment before issuing a prescription. This ensures Mounjaro is safe and suitable for your individual health profile.
How long does it take to get Mounjaro on the NHS waiting list?
This varies dramatically by region. Some areas have waiting times of months; others much longer. Specialist weight management services are under significant demand across the UK. Private prescription is faster — typically assessed and prescribed within days — but involves upfront costs.
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.