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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What Mounjaro Does — How It Works and How to Access It in the UK
Mounjaro (tirzepatide) is a once-weekly injection that works as a dual GIP and GLP-1 receptor agonist, meaning it activates two natural hormone pathways in your body to help regulate appetite and support weight management. Unlike some other weight loss medications, Mounjaro's dual mechanism may help you feel fuller after smaller meals while slowing how quickly food leaves your stomach. This page covers how Mounjaro works, UK costs, and both NHS and private access routes so you can understand your options.
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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 Works and What It Costs in the UK
Mounjaro works by activating GIP (glucose-dependent insulinotropic polypeptide) and GLP-1 (glucagon-like peptide-1) receptors — two natural hormone pathways that regulate hunger and blood sugar. This dual mechanism is what distinguishes tirzepatide from other GLP-1 medications like Wegovy (semaglutide). Clinical trials showed that Mounjaro helped participants lose an average of 15–21% of their body weight over 72 weeks, though individual results vary significantly.
UK private prescription costs typically range from £129 to £320 per month depending on your dose. The Mounjaro KwikPen comes in six doses (2.5 mg, 5 mg, 7.5 mg, 10 mg, 12.5 mg, and 15 mg), and most people start at 2.5 mg, increasing gradually every four weeks. Prices vary between providers, so it's worth comparing before starting treatment. All private prescriptions require a clinical assessment from a UK-licensed prescriber.
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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
Everything you need to understand your weight, explore medication options, and track your progress — completely free.
NHS vs Private Access — How to Get Mounjaro in the UK
NHS access: Mounjaro is approved by NICE for NHS specialist weight management services, but access is limited and varies significantly by region. You'll need referral from your GP to a tier 3 or tier 4 weight management service — waiting lists can be several months to over a year in many areas. Eligibility typically requires a BMI of 30 or above, or 27–29.9 with weight-related health conditions.
Private access: Available through GPhC-registered online pharmacies without NHS referral. You'll complete an online health questionnaire and consultation with a UK-licensed prescriber, who will assess whether Mounjaro is suitable. If approved, your prescription is dispensed by post. This route is faster (typically within days) but comes at the costs mentioned above. Use our free GLP-1 weight loss calculator to estimate potential outcomes at different doses.
- 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 exactly does Mounjaro do in your body?
Mounjaro activates two hormone pathways (GIP and GLP-1) that reduce appetite, help you feel fuller after eating, and slow stomach emptying. It's a prescription injection you take once weekly. Clinical trials showed average weight loss of 15–21% of body weight, but results vary between individuals.
How much does Mounjaro cost on the NHS in the UK?
Mounjaro is available through NHS specialist weight management services, but it's not available on standard GP prescription. Access is through tier 3/4 services with significant regional variation and waiting lists. Check with your local Integrated Care Board for availability in your area.
How much does private Mounjaro prescription cost in the UK?
Private prescription costs typically range from £129 to £320 per month depending on your dose and provider. Costs are higher at maximum doses (15 mg). Each Mounjaro KwikPen contains four weekly doses. Compare providers before choosing — prices vary.
How do I get a private Mounjaro prescription in the UK?
Access private Mounjaro through GPhC-registered online pharmacies. Complete an online health questionnaire and consultation with a UK-licensed prescriber. If approved, your prescription is dispensed by post. This typically takes 3–7 days. You'll need a valid UK prescription from a licensed healthcare provider.
Is Mounjaro cheaper than Wegovy in the UK?
Costs are similar — both range from approximately £129–£320 per month privately, depending on dose. Mounjaro may have slightly different pricing at certain doses. The dual mechanism of Mounjaro (vs Wegovy's single GLP-1 mechanism) may affect individual outcomes, but clinical trial data showed comparable average weight loss percentages.
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.