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
Mounjaro Side Effects, NHS Access & UK Costs
Mounjaro (tirzepatide) is a prescription-only GLP-1 and GIP receptor agonist injection licensed for weight management in the UK. Understanding both the potential side effects and how to access it through NHS or private routes helps you make an informed decision. This guide covers what side effects to expect, how the NHS prescribes Mounjaro, and the cost differences between accessing it through the health service or private online prescription routes. Individual responses vary significantly.
10,000+ calculations today · NHS-aligned thresholds · 100% free
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.
Mounjaro Side Effects & Private Prescription Costs in the UK
Mounjaro is generally well tolerated, but side effects are common, especially during dose escalation. Very common side effects (affecting more than 1 in 10 people) include nausea, diarrhoea, vomiting, constipation, and stomach pain. These typically improve over time as your body adjusts to each dose level. Common side effects include indigestion, headache, fatigue, dizziness, and injection site reactions like redness or bruising.
Most side effects are manageable and temporary. However, serious side effects requiring urgent medical attention include severe persistent stomach pain spreading to the back (possible pancreatitis), gallbladder problems, serious allergic reactions, and unexplained changes in vision. Always contact your GP or seek emergency care if you experience severe symptoms.
Private prescription costs for Mounjaro in the UK typically range from £150 to £320 per month, depending on the dose strength. At starting dose (2.5 mg), costs are lower; at maximum dose (15 mg), costs are higher. Prices vary between GPhC-registered online pharmacies. Private online consultations with UK-licensed prescribers usually cost £50 to £150 separately, though some providers include this in the overall package.
Clinically BackedWeight Loss
No appointments. No waiting rooms. Just care — from a UK-regulated online pharmacy.
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: How to Access Mounjaro in the UK
NHS access requires referral to a specialist tier 3 or tier 4 weight management service through your GP. NICE has approved tirzepatide for NHS use, but availability varies significantly by region and integrated care board (ICB). Waiting lists can be several months to over a year in many areas. Once prescribed through the NHS, Mounjaro is free on prescription (you pay standard prescription charges, typically £9.90 per item).
Private access is faster — usually available within days to weeks. You complete an online consultation with a UK-licensed prescriber (registered with the GMC or RCGP), receive a prescription if clinically appropriate, and collect from a GPhC-registered pharmacy. No NHS referral needed. Use our free GLP-1 weight loss calculator to project potential outcomes, then discuss suitability with a private prescriber during your consultation.
Q1: What are the most common Mounjaro side effects? A1: Nausea, diarrhoea, vomiting, constipation, and stomach pain are the most common side effects, particularly when starting or increasing your dose. These usually settle within days to weeks as your body adjusts. Taking Mounjaro with food and staying hydrated can help manage these effects. Q2: How much does Mounjaro cost privately in the UK? A2: Private Mounjaro costs range from approximately £150 to £320 per month depending on dose strength, plus a separate online consultation fee (£50–£150). Prices vary between providers. NHS prescription costs are significantly lower — standard prescription charges apply once prescribed. Q3: Can I get Mounjaro on the NHS in the UK? A3: Yes, NICE has approved tirzepatide (Mounjaro) for NHS specialist weight management services. Access requires GP referral to a tier 3 or tier 4 specialist service. Availability and waiting times vary considerably by region. Your GP can advise on local services and referral process. Q4: How long do Mounjaro side effects last? A4: Most side effects improve within a few days to two weeks as your body adjusts to each dose. Nausea and gastrointestinal effects are typically most noticeable in the first week after injection. Serious side effects are rare but require immediate medical attention. Q5: What's the difference between NHS and private Mounjaro access? A5: NHS access is free (or at standard prescription charge) but requires specialist referral and can involve long waiting lists. Private access is faster (days to weeks), available without NHS referral via online consultation, but costs £150–£320 monthly. Your GP can help determine which route is most appropriate for you.- 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 is BMI and how is it calculated?
BMI (Body Mass Index) is calculated by dividing your weight in kilograms by your height in metres squared. It's the standard screening tool used by the NHS to assess whether adults are a healthy weight.
Is BMI accurate for everyone?
BMI is a useful screening tool but doesn't account for muscle mass, bone density, or body fat distribution. Athletes may have a high BMI without excess fat. The NHS recommends using BMI alongside waist circumference for a more complete picture.
What are GLP-1 medications like Mounjaro and Wegovy?
GLP-1 receptor agonists are prescription medications that mimic gut hormones to reduce appetite and help with weight loss. Mounjaro (tirzepatide) and Wegovy (semaglutide) are the two most widely used for weight management in the UK.
Am I eligible for GLP-1 weight loss medication in the UK?
Generally, you need a BMI of 30+ (obese) or 27+ with a weight-related health condition. You must be 18 or over. Use our BMI calculator to check.
What is the difference between Mounjaro and Wegovy?
Mounjaro (tirzepatide) is a dual GIP/GLP-1 agonist with up to 22.5% weight loss. Wegovy (semaglutide) is GLP-1-only with up to 15-17% weight loss. Both are weekly injections.
Is this website free to use?
Yes, 100% free. No sign-up required. All tools work instantly in your browser and no personal data is stored on our servers.
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.