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 Warnings — What You Need to Know
Mounjaro (tirzepatide) is a prescription-only weight management injection available in the UK, but like all medications, it has important warnings and safety considerations you should understand before starting. This guide covers the key warnings, who shouldn't take Mounjaro, potential serious side effects, how it compares to alternatives like Wegovy, and how to access it safely through either NHS specialist services or private prescription routes. Understanding these warnings helps you make an informed decision about whether this treatment is right for you.
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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.
Important Mounjaro Warnings and Safety Concerns
Contraindications (who cannot take Mounjaro): Do not use Mounjaro if you are under 18, pregnant, planning pregnancy, or breastfeeding. It is also unsuitable if you have a personal or family history of medullary thyroid carcinoma (MTC) or multiple endocrine neoplasia syndrome type 2 (MEN 2), or if you have a severe allergy to tirzepatide or any ingredients in the KwikPen.
Serious warnings requiring medical attention: Severe, persistent stomach pain spreading to the back may indicate pancreatitis — seek urgent medical care. Changes in vision may signal diabetic retinopathy complications, particularly in people with existing type 2 diabetes. Signs of serious allergic reaction (facial swelling, difficulty breathing, throat tightness) require emergency care. Gallbladder problems, including gallstones, have been reported more frequently with GLP-1 and GIP/GLP-1 medications.
Important monitoring: Your prescriber will assess your individual health history before issuing a Mounjaro UK prescription. Those with a personal or family history of thyroid cancer require particularly careful evaluation, as GLP-1 and GIP/GLP-1 receptor agonists stimulate thyroid C-cell growth in animal studies, though clinical relevance in humans remains unclear.
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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.
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NHS Access vs Private Routes — Cost and Safety
NHS route: Mounjaro is NICE-approved for use within NHS specialist tier 3 weight management services. Access is through referral from your GP, with assessment and prescription managed by specialist services. Availability varies significantly by region and integrated care boards (ICBs). Waiting lists can extend many months in some areas. Once prescribed, NHS supply is typically at no direct cost to you.
Private online route: Available through GPhC-registered pharmacies following online clinical consultation with a UK-licensed prescriber. This route does not require NHS referral and typically has shorter wait times. Private Mounjaro costs vary by dose and provider, generally ranging from £120–£280 per month depending on whether you're at starting dose (2.5 mg) or higher maintenance doses (up to 15 mg). Always verify the prescriber is UK-licensed and the pharmacy is GPhC-registered before proceeding.
- 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 warnings with Mounjaro?
The most serious warnings include acute pancreatitis (severe back pain), diabetic retinopathy worsening, serious allergic reactions, and gallbladder complications. Mounjaro is contraindicated in personal or family history of medullary thyroid cancer. Always seek urgent medical attention if you experience severe stomach pain, vision changes, or breathing difficulty whilst on Mounjaro.
Can I get Mounjaro through the NHS in the UK?
Yes, Mounjaro is NICE-approved for NHS use through specialist tier 3 weight management services. You need a GP referral to access NHS specialist services. Availability and waiting times vary significantly by region. Once prescribed through NHS services, there is no direct cost, but access can be limited in some areas.
How much does private Mounjaro cost in the UK?
Private Mounjaro costs typically range from £120–£280 per month depending on dose and provider. Starting doses (2.5 mg) are generally cheaper than higher maintenance doses (15 mg). Costs vary between private prescribing services, so comparing options is recommended before committing to treatment.
What's the difference between Mounjaro warnings and Wegovy warnings?
Both are GLP-1 receptor agonists with similar warnings (pancreatitis, gallbladder, retinopathy risk). Mounjaro is a dual GIP/GLP-1 agonist, whilst Wegovy is GLP-1-only, so mechanism differs slightly. Both share thyroid cell concerns. Your prescriber will assess which is more appropriate for your individual health profile.
How do I know if I'm eligible for Mounjaro in the UK?
General eligibility requires BMI of 30 or above, or 27–29.9 with weight-related health conditions (diabetes, hypertension, sleep apnoea). South Asian, Chinese, Black African, and Caribbean adults may qualify at lower BMI. A prescriber will conduct a full clinical assessment before confirming eligibility and issuing a prescription.
Ready to take control of your weight loss journey?
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