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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How to Purchase Mounjaro in the UK — Mounjaro vs Wegovy Comparison
If you're considering prescription weight loss treatment in the UK, you may be weighing up Mounjaro (tirzepatide) and Wegovy (semaglutide). Both are licensed prescription-only weight management injections available in the UK, but they work differently and have distinct clinical profiles. This guide breaks down the key differences to help you understand what each medication offers, so you can have an informed conversation with your GP or prescriber about which option might be right for you.
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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.
How Mounjaro and Wegovy Work — Clinical Mechanism Differences
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, meaning it activates two natural hormone pathways in your body. This dual mechanism may help regulate appetite, reduce food cravings, and support feelings of fullness more effectively than single-action medications.
Wegovy (semaglutide) is a GLP-1 receptor agonist only — it activates a single hormone pathway. Both medications slow gastric emptying and signal fullness to the brain, but Mounjaro's dual action is the key structural difference.
In the SURMOUNT-1 clinical trial, Mounjaro at the maximum dose (15 mg once weekly) achieved average weight loss of approximately 20.9% of body weight over 72 weeks alongside diet and exercise. In the STEP-1 clinical trial, Wegovy at maximum dose (2.4 mg once weekly) achieved approximately 14.9% average weight loss at 68 weeks. However, individual results vary significantly, and these are trial averages — not assured outcomes for any individual.
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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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Dosing, Eligibility, and How to Access Both in the UK
Mounjaro starts at 2.5 mg once weekly and escalates in 2.5 mg increments up to a maximum of 15 mg. Wegovy starts at 0.25 mg and escalates to a maximum of 2.4 mg. Both require a prescription and clinical assessment before dispensing.
Eligibility is the same for both: adults with a BMI of 30 kg/m² or above, or BMI 27–29.9 with weight-related health conditions (type 2 diabetes, high blood pressure, cardiovascular disease, sleep apnoea, or dyslipidaemia). Adults of South Asian, Chinese, Black African, or Black Caribbean descent may qualify at lower BMI thresholds (from BMI 27.5). Your GP or prescriber will assess which option, if either, is suitable for your individual health profile. Both are available through NHS specialist weight management services or via private online prescribing following a clinical consultation.
Which Should You Choose — A Decision for Your PrescriberThe choice between Mounjaro and Wegovy is not about superiority — it's about individual suitability. Some prescribers may recommend Mounjaro's dual mechanism if single-action therapy hasn't been effective; others may suggest Wegovy as a well-established first-line option. Factors like your medical history, other medications, previous weight loss attempts, and personal preferences all matter.
Use our free BMI calculator above to confirm your eligibility category, and our GLP-1 weight loss calculator to explore potential outcomes at different doses for both medications. These tools help you understand the landscape before you speak to your GP. Neither medication works without a prescription, clinical assessment, and commitment to dietary and lifestyle changes alongside the injection.
- 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 main difference between Mounjaro and Wegovy?
Mounjaro is a dual GIP and GLP-1 agonist (two hormone pathways), while Wegovy is a GLP-1 agonist only (one pathway). Mounjaro has a higher starting dose and maximum dose (2.5–15 mg) compared to Wegovy (0.25–2.4 mg). Clinical trials suggest Mounjaro achieved slightly higher average weight loss, but results vary individually.
Can I switch from Wegovy to Mounjaro on the NHS?
NHS availability varies significantly by region. Some specialist weight management services may offer both; others may offer one or neither. Discuss switching options with your NHS specialist if enrolled in a weight management programme. Private prescribers can assess either or both options after a clinical consultation.
How much does Mounjaro cost to purchase privately in the UK?
Private Mounjaro costs vary by dose and provider, typically ranging from £129–£320 per month depending on the dose and dispensary. Prices differ based on whether you're on a lower starting dose (2.5 mg) or a higher maintenance dose (10–15 mg). Always check with the prescriber or pharmacy for exact pricing.
Is Mounjaro available on the NHS in the UK?
NICE has approved tirzepatide (Mounjaro) for use within NHS tier 3 specialist weight management services. However, NHS availability is very limited and varies by region. Waiting lists for NHS specialist services can be very long in many areas. Private prescription is the faster route for most people.
Which injection requires fewer doses — Mounjaro or Wegovy?
Both Mounjaro and Wegovy are once-weekly injections, so they're equal in injection frequency. The difference is in escalation timeline — Mounjaro escalates every 4 weeks in 2.5 mg increments, while Wegovy escalates every 4 weeks in smaller 0.25–0.5 mg increments. Maximum dose is reached faster with Mounjaro (around 20 weeks) than Wegovy (around 16 weeks).
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.