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
Free tracker included with every download this week
Is Mounjaro Safe in the UK?
Mounjaro (tirzepatide) is a prescription-only weight management injection that has been approved by UK health authorities for adults with obesity or overweight with weight-related health conditions. Like all medications, it has both benefits and potential side effects that your GP or prescriber will assess before prescribing. This guide explains Mounjaro's safety profile, what to expect, how to access it in the UK, and what it costs through NHS and private routes.
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Calculate Your BMI Instantly
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.
Safety Profile and Side Effects
Mounjaro has been rigorously tested in clinical trials (the SURMOUNT programme) and is subject to additional MHRA monitoring via Black Triangle ▼ status, meaning safety data is continuously reviewed. Most common side effects are gastrointestinal — nausea, diarrhoea, constipation, and stomach pain affect more than 1 in 10 people, particularly when starting or increasing doses.
- Very common: nausea, vomiting, diarrhoea, constipation, abdominal pain
- Common: indigestion, acid reflux, injection site reactions, fatigue, dizziness, hair loss
- Uncommon but serious: severe pancreatitis (persistent stomach pain spreading to back), gallbladder problems, serious allergic reactions
Side effects typically improve over time as your body adjusts. Your prescriber will monitor you and may adjust your tirzepatide dose if side effects are severe. Always seek urgent medical attention if you experience severe stomach pain, difficulty breathing, or signs of serious allergic reaction.
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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.
UK Access Routes and Costs
In the UK, Mounjaro can be accessed through two routes: NHS specialist services (free but with waiting lists) or private online prescribing (fast access but at cost). NHS access requires referral to a tier 3 weight management service by your GP, though availability varies significantly by region — some areas have waiting lists of several months. Private costs typically range from £129–£320 per month depending on your dose, with higher doses costing more. Before prescribing, any UK-licensed prescriber will conduct an online clinical assessment to confirm you meet eligibility criteria: BMI ≥30, or BMI 27–29.9 with weight-related conditions like type 2 diabetes or high blood pressure.
- 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 safe to use long-term in the UK?
Mounjaro has been approved for use in the UK with ongoing MHRA safety monitoring (Black Triangle status). It's designed for long-term weight management, though your GP or prescriber will review your suitability regularly. Individual factors determine safe use — always inform your prescriber of all health conditions and medications.
What serious side effects should I watch for?
Seek urgent medical attention for: severe stomach pain spreading to the back (possible pancreatitis), serious allergic reactions (swelling of face/lips/throat), gallbladder symptoms (upper right abdominal pain), or changes in vision. Most people experience only mild gastrointestinal side effects that improve over time.
How much does Mounjaro cost privately in the UK?
Private costs typically range from £129–£320 monthly depending on your dose. Each KwikPen contains 4 weeks' supply. Prices vary between prescribing services — shop around. NHS access is free but requires specialist referral with potential waiting lists.
How do I get Mounjaro safely on the NHS in the UK?
Ask your GP for referral to your local tier 3 weight management service. They'll assess your eligibility (BMI and health conditions), conduct a clinical assessment, and manage your treatment including dose titration and monitoring. Availability varies regionally.
What's the difference between Mounjaro and Wegovy for safety?
Both are safe GLP-1-type medications approved in the UK with similar common side effects (nausea, diarrhoea). Mounjaro is a dual GIP/GLP-1 receptor agonist, whilst Wegovy is GLP-1 only — clinical trial data shows comparable safety profiles. Your prescriber will assess which suits you individually.
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.