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 considering switching from Wegovy to Mounjaro, understanding the cost and access routes in the UK is essential. Both are prescription-only weight management medications, but they work differently and have different availability options. Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, while Wegovy (semaglutide) is a GLP-1 agonist only. This guide covers what you need to know about accessing either medication, typical costs, and how to discuss switching with a prescriber.
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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.
UK Cost And Access Routes For Both Medications
Wegovy and Mounjaro have different costs depending on whether you access them through the NHS or privately in the UK.
- Private prescriptions: Wegovy typically costs between £130–£300 per month depending on your dose and provider. Mounjaro costs similarly, usually £150–£320 per month. Both are supplied as pre-filled pens (Wegovy as auto-injection pens, Mounjaro as a KwikPen device). You'll need a valid UK prescription from a licensed prescriber following an online clinical assessment.
- NHS access: Both medications are available through NHS specialist tier 3 weight management services, but only after GP referral and assessment. NHS availability varies dramatically by region and ICB (Integrated Care Board), with significant waiting lists in many areas. NHS prescriptions use the standard NHS prescription charge (currently £9.90 per prescription if eligible, or free if exempt).
- Online prescribing: Both can be prescribed through UK-licensed online prescribers following a consultation. These services are private and costs are similar to pharmacy prices above. Mounjaro must be dosed carefully with dose titration starting at 2.5mg and escalating over weeks, while Wegovy also involves gradual dose escalation from 0.25mg.
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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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When To Switch And How To Access The Alternative
If you're switching from Wegovy to Mounjaro or vice versa, a prescriber must manage the transition — do not stop one medication and start another without guidance. Your GP or private prescriber will assess whether switching is appropriate based on your response, side effects, and health status. There's no official NHS dose conversion chart between Mounjaro and Wegovy, but approximate equivalences exist: 5mg Mounjaro approximates to 0.5mg Wegovy, 10mg Mounjaro to 1.7mg Wegovy, and 15mg Mounjaro to 2.4mg Wegovy. Use our free GLP-1 weight loss calculator to estimate potential outcomes at different doses, and our BMI calculator to track how your weight relates to UK health guidelines during your treatment journey.
- 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.
What's the actual cost difference between Wegovy and Mounjaro in the UK?
Private costs are comparable—both typically range £130–£320 monthly depending on dose and provider. Wegovy auto-injection pens and Mounjaro KwikPen devices have similar pricing. NHS costs are £9.90 per prescription (or free if exempt), but NHS access is limited and varies by region. Individual pricing depends on your starting dose and titration schedule.
Can I switch from Wegovy to Mounjaro on the NHS?
Potentially, but NHS access to either medication requires specialist referral through tier 3 weight management services. Switching between medications must be managed by your NHS prescriber or GP. Availability and switching policies vary significantly by ICB. Contact your local NHS weight management service or GP to discuss switching options.
How long does it take to get Wegovy or Mounjaro privately in the UK?
Private prescriptions are typically issued within 1–2 days of completing an online clinical assessment with a UK-licensed prescriber. The medication is then dispatched by the pharmacy, usually arriving within 2–5 working days. This is much faster than NHS routes, where waiting lists for specialist services can be months or years in many areas.
Do I need a new prescription to switch medications?
Yes, you'll need a new prescription from a licensed prescriber to switch from Wegovy to Mounjaro or vice versa. The prescriber will review your health, previous response, side effects, and eligibility before issuing a new prescription. Never switch medications without prescriber guidance—dose titration is different for each drug.
What happens to my dose when I switch from Wegovy to Mounjaro?
Doses don't convert directly—Mounjaro has a lower maximum dose (15mg weekly) than Wegovy's maximum (2.4mg weekly), but they work through different mechanisms. Your prescriber may start you on a similar or different dose depending on your response to Wegovy and individual factors. Mounjaro uses a longer titration schedule starting at 2.5mg, escalating over weeks to find your optimal dose.
Ready to take control of your weight loss journey?
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