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
Is Mounjaro Safe in the UK?
Yes, Mounjaro (tirzepatide) is considered safe for use in the UK when prescribed and monitored appropriately. It's a prescription-only medicine approved by the MHRA and licensed for weight management in UK adults. Like all medications, it has potential side effects, but clinical trials have shown it to be generally well-tolerated. Safety depends on proper medical assessment, appropriate dosing, and following your prescriber's guidance throughout treatment.
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.
What the Safety Evidence Shows
Mounjaro has undergone rigorous clinical testing before UK approval. The SURMOUNT trials, which involved thousands of participants, demonstrated that tirzepatide was generally safe and well-tolerated over extended treatment periods. The MHRA, the UK's medicines regulator, has approved Mounjaro for weight management and continues to monitor its safety through pharmacovigilance systems.
Most side effects reported are mild to moderate and typically occur during the dose titration phase (the first 16–20 weeks when doses are gradually increased). Many side effects, such as nausea and stomach discomfort, tend to reduce as your body adjusts. The most common side effects include nausea, diarrhoea, constipation, and vomiting—these are expected responses to how the medication works in the gut.
Serious side effects are rare but have been reported, including pancreatitis (inflammation of the pancreas), gallbladder problems, and changes in vision. Your GP or prescriber will assess whether Mounjaro is suitable for you based on your individual health history before prescribing.
Clinically BackedWeight Loss
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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 Use Mounjaro
Mounjaro is not suitable for certain groups. You should not use Mounjaro if you are pregnant, planning to become pregnant, or breastfeeding. It's also contraindicated if you have a personal or family history of medullary thyroid cancer or multiple endocrine neoplasia syndrome type 2 (MEN2). Those with severe gastroparesis (stomach paralysis) or a history of pancreatitis need careful medical assessment before use.
People taking insulin or certain diabetes medications may need dose adjustments—your prescriber will discuss this. If you have a tirzepatide allergy or if weight loss injections are unsuitable for your specific health circumstances, your GP or licensed prescriber will recommend alternative approaches instead. Always disclose your full medical history during your clinical assessment.
- 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 approved by the MHRA in the UK?
Yes, Mounjaro (tirzepatide) is fully approved by the MHRA for weight management in UK adults. It's subject to additional monitoring (Black Triangle status), meaning the MHRA closely tracks safety data. This doesn't indicate it's unsafe—it's standard practice for newer medications to ensure ongoing safety surveillance.
What are the most common side effects of Mounjaro?
The most common side effects are nausea, diarrhoea, constipation, vomiting, and stomach pain. These are usually mild to moderate and often improve within the first few weeks as your body adjusts. Nausea tends to be most noticeable at the start of treatment and during dose increases.
Can I use Mounjaro if I have type 2 diabetes?
Yes, many people with type 2 diabetes use Mounjaro safely for weight management. However, if you're taking diabetes medications like insulin or sulphonylureas, your prescriber may need to adjust your doses. Always inform your prescriber of all medications you take so they can assess your individual safety.
How can I check if Mounjaro is safe for me personally?
A licensed prescriber will assess your safety through a detailed clinical consultation. They'll review your medical history, current medications, allergies, and health conditions. Use our free BMI calculator and GLP-1 weight loss calculator above to understand your health metrics, but always discuss prescription options with a healthcare professional.
What should I do if I experience side effects?
Most side effects are mild and temporary. If you experience severe stomach pain (possible pancreatitis), gallbladder symptoms, serious allergic reactions, or changes in vision, seek urgent medical attention. For other side effects, contact your prescriber or GP—they may suggest managing the symptom or adjusting your dose.
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.