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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Side Effects With Mounjaro: UK Access and Cost Guide
Mounjaro (tirzepatide) is a prescription-only weight management injection that works as a dual GIP and GLP-1 receptor agonist. Understanding potential side effects and knowing how to access it in the UK — whether through the NHS or privately — helps you make informed decisions about treatment. This guide covers what side effects to expect, how much Mounjaro costs privately, and your options for getting a prescription in the UK.
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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 Cost Context in the UK
Common side effects with Mounjaro include nausea, diarrhoea, vomiting, and constipation — affecting up to 1 in 3 users, especially when starting or increasing doses. Many side effects improve within a few weeks as your body adjusts. Stomach pain, indigestion, and injection site reactions are also frequently reported. Less common but important side effects include hair loss, fatigue, and dizziness.
Private prescription costs for Mounjaro in the UK typically range from £129 to £320 per month depending on your dose. A Mounjaro KwikPen contains 4 weeks of injections (one pen per month at maintenance doses). Starting doses (2.5 mg) tend to cost less than maximum doses (15 mg). Many private clinics offer dose escalation plans where you pay per dose rather than per full pen, reducing initial costs.
- Starter packs (2.5–5 mg) often cost £129–£180/month
- Mid-range doses (7.5–10 mg) typically £200–£250/month
- Higher doses (12.5–15 mg) may reach £280–£320/month
Private access involves an online consultation with a UK-licensed prescriber, who assesses your eligibility based on BMI and health status. If approved, your prescription is sent to a GPhC-registered pharmacy for dispensing.
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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 Routes: What's the Difference?
The NHS route requires referral to a specialist tier 3 or 4 weight management service through your GP. NICE has approved tirzepatide (Mounjaro) for NHS use, but access varies significantly by region and waiting lists can extend from months to years in many areas. Mounjaro is not routinely available through standard GP prescriptions — only through specialist services.
The private route is faster: you complete an online consultation, receive a prescription decision within days, and collect from a pharmacy. No NHS referral needed. Private costs are your responsibility, though some people use private treatment alongside NHS support. When comparing costs, factor in the consultation fee (typically £25–£50) plus the medication itself. Your GP can advise which route suits your circumstances best.
- 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 serious side effects of Mounjaro I should watch for?
Seek immediate medical attention for severe, persistent stomach pain (possible pancreatitis), serious allergic reactions with swelling of face or throat, gallbladder problems, or unexplained changes in vision. These are rare but require urgent assessment. Contact your GP or call 111 immediately if you experience any of these symptoms during Mounjaro treatment.
How much does a month's supply of Mounjaro cost in the UK privately?
Private Mounjaro costs typically range from £129 to £320 per month in the UK, depending on your dose. Starting doses (2.5–5 mg) cost less, around £129–£180, while maximum doses (15 mg) may cost £280–£320. A single KwikPen contains 4 weeks of injections. Costs vary between different private clinics and pharmacies.
Can I get Mounjaro on the NHS, and how long does it take?
Mounjaro is available on the NHS through specialist tier 3 weight management services, but you need a GP referral. Access and waiting times vary greatly by region — some areas have significant waiting lists of 6–12 months or longer. NICE has approved tirzepatide, but availability depends on your local integrated care board (ICB) funding and capacity.
How do I access Mounjaro privately in the UK?
Book an online consultation with a UK-licensed prescriber through a private clinic. You'll answer health questions and confirm your BMI and medical history. If approved, the prescriber issues a prescription to a GPhC-registered pharmacy for dispensing. The whole process typically takes 3–7 days from consultation to receiving your first pen.
Is Mounjaro the same as Wegovy, and which has fewer side effects?
Mounjaro (tirzepatide) and Wegovy (semaglutide) are different medications — Mounjaro is a dual GIP and GLP-1 agonist, while Wegovy is GLP-1 only. Clinical trials show similar common side effects for both. Individual responses vary; some people tolerate one better than the other. Your prescriber can discuss which might suit you based on your health profile.
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.