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? What You Need to Know
Yes, Mounjaro (tirzepatide) is safe for weight management when prescribed appropriately in the UK. It's an MHRA-approved prescription-only medicine that has undergone rigorous clinical trials. Like all medications, it carries potential side effects and isn't suitable for everyone. Safety depends on proper clinical assessment, medical supervision, and following your prescriber's guidance. Understanding how Mounjaro works, who can take it, and what to expect helps 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.
Mounjaro Safety in the UK — What the Evidence Shows
Mounjaro received MHRA approval in 2023 and is subject to additional monitoring (Black Triangle status), meaning the regulator actively monitors safety data. Clinical trials, including SURMOUNT-1, demonstrated that tirzepatide is effective for weight management when used alongside lifestyle changes. The most common side effects are gastrointestinal—nausea, diarrhoea, vomiting, and constipation—which typically decrease as your body adjusts to the dose. Serious side effects are rare but include pancreatitis (severe stomach pain) and gallbladder issues. Your prescriber will assess your medical history, current medications, and any contraindications before prescribing. Women planning pregnancy must not take Mounjaro due to lack of safety data. People with a personal or family history of thyroid cancer or multiple endocrine neoplasia (MEN2) cannot take it. UK dose titration starts at 2.5 mg weekly, with gradual increases to reduce side effects.
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.
Accessing Mounjaro Safely — NHS vs Private Routes
NHS route: Access through your GP, who may refer you to a specialist weight management service (tier 3 or 4). NHS prescribing follows NICE guidelines for eligibility—BMI 30 or above, or 27+ with weight-related health conditions. Waiting times vary significantly by region; some areas have substantial delays. Private route: Online prescription services offer faster access following a clinical consultation with a UK-licensed prescriber. You'll answer a detailed health questionnaire and may have a video call. If approved, your prescription is sent to a GPhC-registered pharmacy for dispensing. Both routes require clinical assessment—no pharmacy will prescribe without proper medical evaluation. Safety is equally important whether you access Mounjaro through the NHS or privately; the difference is speed and availability, not safety standards.
- 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 if I have type 2 diabetes?
Mounjaro can be safe for people with type 2 diabetes, but your prescriber must know about it. If you take insulin or sulphonylureas, your diabetes medication may need adjusting because Mounjaro affects blood sugar. Always disclose all your medications during your clinical assessment so your prescriber can manage any interactions safely.
What are the serious side effects I should watch for?
Serious side effects are uncommon but include severe stomach pain spreading to the back (possible pancreatitis), gallbladder pain, serious allergic reactions, or vision changes. If you experience these, stop using Mounjaro and seek urgent medical attention. Most users experience only mild gastrointestinal discomfort that improves within days or weeks.
Can I take Mounjaro if I'm on other medications?
Mounjaro may reduce how your body absorbs oral medications. If you take oral contraceptives, add a barrier method or switch to non-oral contraception for 4 weeks after starting and after each dose increase. Always list all current medications during your clinical assessment so your prescriber can identify potential interactions.
How do I know if I'm eligible for Mounjaro on the NHS?
You're generally eligible if your BMI is 30 or above, or 27–29.9 with weight-related health conditions like diabetes, hypertension, or cardiovascular disease. For people of South Asian, Chinese, Black African, or Black Caribbean heritage, lower thresholds apply. Your GP can assess your eligibility during a consultation.
What's the difference between Mounjaro and Wegovy for safety?
Both are safe prescription-only medicines. Mounjaro uses tirzepatide (dual GIP/GLP-1 mechanism), whilst Wegovy uses semaglutide (GLP-1 only). Clinical trial data supports both. The safety profile is similar—mainly gastrointestinal side effects. Your prescriber will recommend whichever is more suitable based on your health, availability, and personal factors.
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.