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 Injection Side Effects in the UK — Cost and Access
Mounjaro (tirzepatide) is a once-weekly weight loss injection licensed in the UK that may help adults with obesity or overweight manage their weight. If you're considering this weekly weight loss injection, understanding both the side effects and how to access it — including costs and the prescription route — is essential. This guide explains what to expect, how to get Mounjaro in the UK, and the differences between NHS and private access. Our BMI calculator can help you check whether you might be eligible.
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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 UK Access Routes
Mounjaro is prescription-only and requires a clinical assessment before being prescribed. Common side effects include nausea, diarrhoea, constipation, and stomach pain — typically more frequent at the start of treatment and often improve over time. Less common side effects include fatigue, dizziness, injection site reactions, and hair loss. Serious side effects (such as pancreatitis) are rare but require immediate medical attention.
In the UK, you can access Mounjaro through two main routes:
- NHS: Referral to a specialist tier 3 weight management service through your GP. Availability and waiting times vary significantly by region (ICB). Some areas have substantial waiting lists.
- Private: Online prescription through a UK-licensed prescriber followed by dispensing from a GPhC-registered pharmacy. This route is faster and does not require NHS referral, though it involves direct cost to you.
Both routes require clinical assessment to confirm suitability based on your health, medications, and BMI.
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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 Private Cost and What to Expect
Private Mounjaro typically costs between £150–£300 per month depending on your dose and the provider. Starting doses (2.5 mg and 5 mg) are usually cheaper; higher maintenance doses (10–15 mg) cost more. Some private providers offer package pricing for larger initial commitments.
The private prescription process involves: completing an online health questionnaire, being assessed by a UK prescriber (usually a pharmacist or doctor), receiving a prescription if approved, and having your KwikPen delivered to your address. The whole process typically takes 3–7 days. Our GLP-1 weight loss calculator can help you estimate potential outcomes at different doses, though always remember that individual results vary significantly.
NHS access involves referral from your GP to a specialist service, where you'll have a fuller assessment including blood tests and monitoring. NHS prescription is free (standard NHS prescription charge £9.90 if you pay per item), but accessing the service can take months in some regions. Private access is faster but costs significantly more. Your choice depends on your urgency, budget, and local NHS availability. Always discuss options with your GP before pursuing private prescription.
- 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 in the UK?
Nausea, diarrhoea, constipation, and stomach pain are the most common side effects, especially during the first few weeks of treatment. These typically improve as your body adjusts. Less common effects include fatigue, dizziness, and injection site reactions. Serious side effects like pancreatitis are rare but require urgent medical attention.
How much does Mounjaro cost privately in the UK?
Private Mounjaro typically costs £150–£300 per month depending on your dose. Starting doses are cheaper; maximum maintenance doses (15 mg) cost more. Costs vary between providers, and some offer package deals. Always confirm pricing before starting treatment. NHS prescription is free but requires referral and may involve waiting lists.
Can I get Mounjaro on the NHS in the UK?
Yes, Mounjaro is NICE-approved for NHS specialist weight management services. Access is through referral from your GP to a tier 3 weight management service. Availability and waiting times vary significantly by region (ICB). Some areas have very long waiting lists. Ask your GP about local specialist services and estimated waiting times.
What's the difference between NHS and private Mounjaro access?
NHS access is free (after standard prescription charge) but involves waiting, GP referral, and a specialist assessment. Private access is faster (3–7 days) and doesn't require NHS referral, but costs £150–£300 monthly. Both require clinical assessment. Your choice depends on urgency, budget, and local NHS availability.
How long does the private Mounjaro prescription process take?
The private online prescription process typically takes 3–7 days from health questionnaire to KwikPen delivery. You'll complete an online assessment, be reviewed by a UK prescriber, receive a prescription if approved, and have your medication delivered. NHS specialist services typically take weeks to months depending on your region's waiting lists.
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.