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 The Mounjaro Jab Safe in the UK?
Yes, Mounjaro (tirzepatide) is approved as safe for use in the UK by the MHRA and is prescribed through NHS specialist weight management services. Like all prescription medications, it does have side effects and is not suitable for everyone—but clinical trials have shown a favourable safety profile when prescribed appropriately. This guide explains what the evidence shows, how the NHS assesses safety, and what you should know before considering this medication.
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 received MHRA approval for weight management in UK adults and is currently subject to additional monitoring (Black Triangle ▼ status), meaning safety data is actively reviewed. The SURMOUNT-1 clinical trial, which included over 500 participants, demonstrated that tirzepatide was well tolerated at doses up to 15 mg weekly.
- Most side effects were mild to moderate and decreased over time as the body adjusted
- The most common side effects were nausea, diarrhoea, and constipation—typically manageable and temporary
- Serious side effects (pancreatitis, severe allergic reactions) were rare
- Withdrawal rates due to side effects were low compared to other weight loss medications
However, individual safety depends on your medical history, current medications, and whether you meet NHS eligibility criteria. Your GP or prescriber conducts a full clinical assessment before prescribing.
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.
How the NHS Determines If It's Safe for You
The NHS uses NICE guidance and a tiered assessment process to ensure Mounjaro is prescribed safely. Specialist tier 3 weight management services evaluate your health conditions, medications, contraindications, and weight-related complications before issuing a prescription. This includes blood tests and discussion of your medical history.
- You cannot take Mounjaro if you're pregnant, breastfeeding, or under 18
- It's not suitable if you have severe gastroparesis or a personal/family history of medullary thyroid cancer
- Interactions with oral contraceptives and some diabetes medications require management
Use our free BMI calculator above to check your starting point, and discuss with your GP whether specialist referral is 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.
Is Mounjaro safe according to the MHRA?
Yes. Mounjaro received MHRA approval for weight management and is on the UK market. It carries additional monitoring status (Black Triangle ▼), meaning the regulator actively reviews safety reports. This is a standard safety measure, not a warning sign.
What are the most common side effects and are they dangerous?
Nausea, diarrhoea, and constipation are most common and usually mild. They typically reduce after a few weeks as your body adjusts. Serious side effects are rare. Most people who experience side effects find them manageable.
Can I take Mounjaro if I have other health conditions?
It depends on your specific conditions. Your prescriber will assess contraindications—for example, it's not suitable if you've had medullary thyroid cancer. Always declare all medical conditions and current medications during your clinical assessment.
Is Mounjaro safer than other weight loss injections like Wegovy?
Both Mounjaro (tirzepatide) and Wegovy (semaglutide) are approved and safe when prescribed appropriately. Mounjaro uses a dual mechanism and may differ in side effect profile. Your prescriber will advise which is more suitable for you.
What should I do if I experience serious side effects?
Contact your GP or NHS 111 immediately if you experience severe stomach pain (possible pancreatitis), serious allergic reactions, or changes in vision. Do not continue the injection and seek medical advice urgently. Your prescriber can adjust your dose or discontinue treatment if needed.
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.