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 and UK Costs Explained
Mounjaro (tirzepatide) is a prescription-only weight management injection available in the UK, but understanding both its side effects and cost is essential before deciding if it's right for you. Side effects are common during the first few weeks and often improve over time, whilst costs vary significantly depending on whether you access treatment through the NHS or privately. This guide explains what to expect, how much it costs, and how to access it 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.
What Are the Most Common Mounjaro Side Effects?
Mounjaro side effects are usually mild to moderate and tend to decrease as your body adjusts to the medication. Very common side effects (affecting more than 1 in 10 people) include nausea, diarrhoea, vomiting, constipation, and stomach pain—particularly when starting or increasing doses. Common side effects include indigestion, acid reflux, injection site reactions (redness or bruising), fatigue, dizziness, and hair loss. Most gastrointestinal side effects settle within a few weeks as your body adapts. However, some people experience persistent nausea or digestive changes throughout treatment. More serious side effects are rare but include severe abdominal pain (possible pancreatitis), gallbladder problems, or serious allergic reactions—seek urgent medical attention if these occur. Side effects often improve as the dose stabilises, and staying hydrated and eating smaller, frequent meals can help manage nausea and digestive symptoms.
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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.
Mounjaro Cost and Access in the UK
NHS access: Mounjaro is available through NHS specialist tier 3 weight management services, but access is limited and varies by region. Waiting times can be several months to over a year in many areas. Your GP can refer you to your local service, though not all ICBs (integrated care boards) currently fund it. Private access: Through GPhC-registered online pharmacies following an online clinical assessment with a UK-licensed prescriber, costs range from approximately £129–£320 per month depending on dose. Private access is faster (typically 1–2 weeks from consultation to delivery) and doesn't require NHS referral. Both routes require a clinical assessment to confirm you meet eligibility criteria, including a BMI of 30 or above, or 27–29.9 with weight-related health conditions. Use our free BMI calculator to check your starting point, and our GLP-1 weight loss calculator to project potential results 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.
How long does it take for Mounjaro side effects to stop?
Most gastrointestinal side effects—nausea, diarrhoea, constipation—typically improve within 2–4 weeks as your body adjusts. However, some people experience lingering nausea or appetite changes throughout treatment. Side effects often improve further once you reach your maintenance dose and your body fully adapts.
What's the difference between NHS and private Mounjaro in the UK?
NHS Mounjaro is free at point of use but involves lengthy waiting times (often 6–12 months) and requires referral to a specialist tier 3 service with regional availability limits. Private Mounjaro requires a clinical assessment fee and ongoing costs (£129–£320/month depending on dose) but is faster (1–2 weeks) and doesn't require NHS referral.
Can I switch from Mounjaro to Wegovy if I get side effects?
Yes, if Mounjaro side effects are intolerable, your prescriber may switch you to Wegovy (semaglutide), which uses a different mechanism (GLP-1 only vs Mounjaro's dual GIP+GLP-1). However, switching requires clinical guidance and timing—you cannot simply switch doses between the two medications.
What is the total cost of Mounjaro treatment in the UK privately?
Private costs depend on your maintenance dose. Starting at 2.5 mg (£129–£160/month) and increasing over 4 weeks to your target dose. At maximum dose (15 mg), costs range from £250–£320/month. Titration typically takes 16–20 weeks, so first-year private cost is approximately £2,000–£3,000 depending on dose progression and provider.
Do I need a prescription from my GP to access private Mounjaro?
No. You can access private Mounjaro through an online consultation with a UK-licensed prescriber (no GP referral needed). The prescriber will assess your eligibility, issue a prescription if appropriate, and it's dispensed by a GPhC-registered pharmacy. However, informing your GP is recommended for safety and medical record purposes.
Ready to take control of your weight loss journey?
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