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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Mounjaro Side-Effects, Cost and UK Access Guide
Mounjaro (tirzepatide) is a prescription-only weight loss injection that may help eligible adults lose weight alongside diet and exercise. Understanding the potential side-effects and knowing your options for accessing it through the NHS or privately in the UK is important before starting treatment. This guide covers what to expect, how much it costs privately, and the different routes available to UK patients seeking this medication.
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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.
Mounjaro Side-Effects and Private Costs in the UK
Mounjaro side-effects are usually mild and tend to improve over time as your body adjusts. The most common include nausea, diarrhoea, constipation, vomiting, and stomach pain — affecting more than 1 in 10 people in clinical trials. These digestive effects often reduce after the first few weeks or as your dose increases gradually.
Private prescription costs in the UK typically range from £129 to £320 per month depending on your dose. A standard starting KwikPen (containing 4 weeks of 2.5mg injections) costs around £129–£149. Higher maintenance doses like 10mg or 15mg per KwikPen may cost £249–£320 monthly. These prices vary between private providers and may include or exclude consultation fees. Always check what's included in the quoted price, as some providers charge separately for the initial online clinical assessment (usually £15–£30).
Serious side-effects are rare but include severe stomach pain (possible pancreatitis), severe allergic reactions, and changes in vision. Seek immediate medical attention if these occur. Common side-effects like headache, fatigue, dizziness, and injection site reactions typically resolve within days or weeks.
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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: What You Need to Know
NHS access to Mounjaro is available through specialist tier 3 and 4 weight management services following NICE approval, but access is limited and varies significantly by region. Your GP can refer you, though waiting lists in many areas extend 6–18 months. Once approved, the NHS provides medication at no cost to you.
Private prescription is faster — you complete an online consultation with a UK-licensed prescriber, usually receive a decision within 24 hours, and can start treatment immediately if approved. No GP referral is needed. Private providers typically assess your BMI, medical history, and current medications before issuing a prescription to a GPhC-registered pharmacy.
Use our free GLP-1 weight loss calculator to estimate potential outcomes at different doses, and our BMI calculator to check your eligibility based on current guidelines.
NHS access to Mounjaro is available through specialist tier 3 and 4 weight management services following NICE approval, but access is limited and varies significantly by region. Your GP can refer you, though waiting lists in many areas extend 6–18 months. Once approved, the NHS provides medication at no cost to you.
Private prescription is faster — you complete an online consultation with a UK-licensed prescriber, usually receive a decision within 24 hours, and can start treatment immediately if approved. No GP referral is needed. Private providers typically assess your BMI, medical history, and current medications before issuing a prescription to a GPhC-registered pharmacy.
Use our free GLP-1 weight loss calculator to estimate potential outcomes at different doses, and our BMI calculator to check your eligibility based on current guidelines.
- 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 are the most common Mounjaro side-effects?
The most common side-effects are nausea, diarrhoea, constipation, vomiting, and stomach pain. These affect more than 1 in 10 people and usually improve within the first few weeks as your body adjusts. Taking injections on a full stomach and staying hydrated may help reduce nausea.
How much does Mounjaro cost privately in the UK?
Private costs range from £129–£320 per month depending on your dose and provider. A starting 2.5mg KwikPen typically costs £129–£149, while higher doses (10mg–15mg) cost £249–£320. Some providers charge additional consultation fees (£15–£30). Always confirm the total cost before committing.
Can I access Mounjaro through the NHS in the UK?
Yes, but only through specialist tier 3 or tier 4 weight management services following referral from your GP. NICE has approved tirzepatide (Mounjaro) for NHS use, but availability and waiting times vary significantly by region. Some areas have waiting lists of 6–18 months.
What's the difference between NHS and private prescription for Mounjaro?
NHS access is free but involves referral, assessment, and potentially long waiting lists. Private prescription is quicker (decision within 24 hours) and doesn't require GP referral, but you pay monthly costs. Both require a clinical assessment to confirm eligibility based on BMI and health conditions.
When should I seek medical help for Mounjaro side-effects?
Contact your GP or seek urgent care if you experience severe, persistent stomach pain (possible pancreatitis), serious allergic reactions (swelling of face or throat), severe vomiting preventing hydration, or changes in vision. Most common side-effects are mild and resolve naturally.
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.