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
If you're currently taking Wegovy and considering a switch to Mounjaro, you'll want to understand the cost and access differences between the two medications. Both are prescription-only weight management injections licensed in the UK, but they differ in mechanism, dosing, and availability. This guide explains how to make the switch, what it costs, and how to access Mounjaro through NHS or private prescription routes.
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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: Wegovy vs Mounjaro in the UK
Wegovy (semaglutide) costs approximately £150–£200 per month through private prescription, depending on your current dose and the pharmacy. It's a GLP-1 receptor agonist available once-weekly as a pre-filled injection pen.
Mounjaro (tirzepatide) costs roughly £130–£250 per month privately, also depending on your dose. As a dual GIP and GLP-1 receptor agonist, it works through a slightly different mechanism, which some clinical evidence suggests may support greater weight loss on average.
NHS access to both medications is limited and varies significantly by region. Both require referral to tier 3 specialist weight management services, and waiting times can be months or years in many areas. Private prescription pathways offer faster access: you can consult a UK-licensed prescriber online, receive a prescription if clinically appropriate, and have it dispensed by a GPhC-registered pharmacy within days.
If you're switching between medications, your prescriber will manage the transition carefully—typically involving a gap between your last Wegovy dose and starting Mounjaro, rather than overlapping doses.
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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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How to Switch: Process and What to Expect
If you're on Wegovy and want to switch to Mounjaro, the process is straightforward. You'll need a new prescription from a UK-licensed prescriber—either through your GP (if they're willing to prescribe), or via a private online consultation with a registered prescriber. During the assessment, your prescriber will review your current weight loss progress, any side effects you've experienced, and whether Mounjaro is suitable for you.
You cannot simply switch pens without medical guidance. Mounjaro uses a different dosing schedule (starting at 2.5 mg and titrating up to 15 mg maximum), whereas Wegovy starts at 0.25 mg and goes up to 2.4 mg. Your prescriber will determine the appropriate starting dose for Mounjaro based on your individual health and previous response to Wegovy. Most people find the transition straightforward, though some experience initial nausea as their body adjusts to the new medication. Keep tracking your progress using our free progress tracker to monitor how Mounjaro works for you after switching.
Once you have a Mounjaro prescription, costs depend on your chosen dose and supplier. At lower doses (2.5–5 mg), private prescription costs tend to be slightly lower than at higher doses. Some private prescribers offer loyalty discounts or package pricing if you're committed to ongoing treatment. NHS Mounjaro is available through specialist weight management services but typically only after you've tried other interventions or meet specific criteria. Our GLP-1 weight loss calculator can help you understand potential outcomes and whether a switch might be worth exploring with your prescriber. Always discuss any medication change with a healthcare professional rather than self-switching.
- 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 Mounjaro more expensive than Wegovy in the UK?
Costs are broadly similar—roughly £130–£250 monthly for Mounjaro versus £150–£200 for Wegovy through private prescription. Exact prices vary by dose, pharmacy, and prescriber. Neither is available cheaply on the NHS; access is limited to specialist services with long waiting lists.
Can my GP prescribe Mounjaro if I'm currently on Wegovy?
Some GPs will prescribe GLP-1 medications within specialist weight management pathways, but most require referral to tier 3 services first. If your GP refuses, private prescription via online consultation is often faster—typically available within 1–2 weeks.
Will I lose more weight on Mounjaro than Wegovy?
Clinical trials suggest Mounjaro may support slightly greater average weight loss (approximately 20.9% at the maximum dose versus 14.9% for Wegovy), but individual results vary significantly. Some people lose more on Wegovy; others respond better to Mounjaro. Your prescriber can discuss realistic expectations.
What happens to my Wegovy when I switch to Mounjaro?
You stop Wegovy and wait 3–7 days before starting Mounjaro at a lower starting dose (typically 2.5 mg). Your prescriber will give specific guidance on timing. Do not overlap the injections—always follow your prescriber's switchover instructions.
How do I get a Mounjaro prescription online in the UK?
Book a consultation with a UK-registered online prescriber. You'll answer health questions, have a brief video or phone assessment, and receive a prescription if appropriate. The prescription is then sent to a GPhC-registered pharmacy for dispensing—usually within 1–2 working days.
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.