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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Is Mounjaro Safe? UK Safety Guide
Mounjaro (tirzepatide) is a prescription-only weight management injection licensed and monitored by the MHRA in the UK. Like all medications, it has potential side effects and safety considerations. This guide explains what the NHS and UK healthcare system recommend about Mounjaro safety, who it's suitable for, how it's monitored, and what you should know before discussing it with your GP or prescriber. Understanding the safety profile helps you make an informed decision about whether this medication 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.
NHS Safety Status and MHRA Monitoring
Mounjaro is subject to additional MHRA monitoring in the UK, indicated by a black triangle (▼) symbol on the product information. This is a normal precaution for newer medications and means the MHRA actively collects and reviews safety reports from patients and healthcare professionals.
The medication has undergone rigorous clinical trials (the SURMOUNT programme) before approval. In these trials, common side effects included nausea, diarrhoea, vomiting, and constipation — typically most noticeable when starting or increasing doses. Most side effects are mild to moderate and improve over time as your body adjusts.
- MHRA approved Mounjaro for weight management in UK adults
- Safety data continuously monitored and reviewed
- Healthcare professionals receive updates on safety findings
- Patients can report side effects via the Yellow Card Scheme
NHS specialist tier 3 services have extensive experience prescribing this medication safely, including dose adjustments and managing side effects.
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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.
Who Should Not Take Mounjaro — Safety Exclusions
Mounjaro is not suitable for certain people, and your prescriber will assess these contraindications before prescribing:
- Under 18 years of age
- Pregnant, planning pregnancy, or breastfeeding
- Severe personal or family history of thyroid cancer (medullary thyroid carcinoma)
- Multiple endocrine neoplasia type 2 (MEN2)
- Allergy to tirzepatide or any ingredients
- Severe kidney or liver disease
- Severe gastroparesis or other serious digestive conditions
If you have diabetes, a history of pancreatitis, gallbladder problems, or take other medications, inform your prescriber. They'll assess whether Mounjaro is safe for your individual situation and may adjust your treatment plan accordingly.
- 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.
Is Mounjaro safe to use long-term in the UK?
Yes, Mounjaro can be used long-term under medical supervision. The MHRA has licensed it for weight management, and UK specialist services monitor patients regularly during treatment. Long-term safety data continues to be collected. Your prescriber will assess whether ongoing use is appropriate for your individual health.
What are the most serious side effects of Mounjaro I should watch for?
Serious side effects are rare but include severe stomach pain spreading to the back (possible pancreatitis), gallbladder problems, serious allergic reactions, and changes in vision. Seek immediate medical attention if you experience these symptoms. Most people experience mild side effects like nausea that typically improve within weeks.
Can I take Mounjaro if I have type 2 diabetes?
Yes, Mounjaro can be prescribed to people with type 2 diabetes for weight management. However, if you also take diabetes medications like insulin or sulphonylureas, your doses may need adjusting. Your prescriber will manage this carefully and monitor your blood sugar levels throughout treatment.
Does Mounjaro interact with other medications?
Mounjaro may reduce how quickly your body absorbs oral medications, including the contraceptive pill. If you take oral contraceptives, add a barrier method for four weeks after starting and after each dose increase. Always inform your prescriber about all medications, supplements, and herbal remedies you take.
How is safety monitored if I'm prescribed Mounjaro on the NHS?
NHS tier 3 specialist services monitor your health regularly during Mounjaro treatment through check-ups, blood tests, and symptom assessment. You're reviewed before each dose increase. Patients can also report side effects using the NHS Yellow Card Scheme. This ongoing monitoring ensures the medication remains safe and effective for you.
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.