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 approved as a safe weight management medication in the UK, regulated by the MHRA and aligned with NHS guidance. Like all prescription medicines, it has side effects and eligibility criteria that your GP or prescriber will assess individually. Understanding the safety evidence, what the NHS says, and how it's monitored can help you make an informed decision about whether it's right for you.
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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.
NHS Approval and Safety Evidence
Mounjaro is MHRA-approved and monitored under additional safety protocols (Black Triangle ▼ status), meaning the MHRA actively tracks real-world safety data. NICE (National Institute for Health and Care Excellence) has approved tirzepatide for use within NHS specialist weight management services, recommending it alongside lifestyle changes for eligible adults.
Clinical trial data (SURMOUNT-1) involved over 2,500 participants on Mounjaro, with comprehensive monitoring of safety and side effects. The most common side effects were gastrointestinal — nausea, diarrhoea, and vomiting — which typically reduce as the body adjusts. Serious side effects like pancreatitis are rare but require immediate medical attention if stomach pain develops.
The NHS recommends Mounjaro only after assessment by a tier 3 specialist weight management service, ensuring your GP has reviewed your medical history, current medications, and weight-related health conditions. This gatekeeping approach means safety is prioritised from the start. Calculate your personal health context using our free BMI calculator to understand your eligibility profile.
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 Eligibility and Getting Mounjaro Safely
To access Mounjaro through the NHS, you need a BMI of 30 or above (or 27+ with weight-related conditions like type 2 diabetes, high blood pressure, or sleep apnoea). You must be referred to a specialist tier 3 weight management service by your GP — Mounjaro is not prescribed in general practice.
Safety checks before starting include:
- Blood tests to check kidney and pancreas function
- Blood pressure and heart rate monitoring
- Review of medications that may interact (especially oral contraceptives — barrier contraception is needed for 4 weeks after starting)
- Pregnancy status (not safe during pregnancy)
- History of thyroid problems or pancreatitis
Private prescribing through online services also requires a clinical assessment, though waiting times are shorter. Either route ensures safety monitoring — use our GLP-1 weight loss calculator to project realistic outcomes alongside medical supervision.
- 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 does MHRA approval mean for Mounjaro safety in the UK?
MHRA (Medicines and Healthcare products Regulatory Agency) approval means Mounjaro has met rigorous standards for safety, quality, and efficacy. The Black Triangle (▼) status means the MHRA monitors real-world safety data actively, so any new safety signals are caught quickly. This is not a warning — it's enhanced oversight ensuring patient safety.
Are the side effects of Mounjaro dangerous?
Most side effects are mild to moderate gastrointestinal symptoms (nausea, diarrhoea) that usually settle within weeks as your body adjusts. Serious side effects like pancreatitis are rare. However, severe stomach pain spreading to the back requires urgent medical attention. Always report persistent or severe symptoms to your GP immediately.
Can I get Mounjaro through the NHS in the UK?
Yes, if eligible. You need a BMI of 30+ or 27+ with weight-related health conditions, and referral to a specialist tier 3 weight management service via your GP. NHS availability varies by region, and waiting lists can be long. Private prescribing is faster but requires clinical assessment too.
Is Mounjaro safe if I'm taking other medications?
Mounjaro can interact with some medications, particularly oral contraceptives (which require barrier contraception for 4 weeks after starting or dose increases) and diabetes medicines. Always tell your prescriber all medications you take. They will assess safety and adjust other prescriptions if needed.
How is my safety monitored once I start Mounjaro?
You'll have initial blood tests and ongoing check-ups with your prescriber every 4–6 weeks during dose increases, then regularly during maintenance. Your GP can be involved in monitoring. Report any new symptoms, changes in your health, or concerns between appointments. Our progress tracker helps you log side effects and weight changes to share with your healthcare team.
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.