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
Does Mounjaro Cause Liver Damage?
Mounjaro (tirzepatide) has not been shown to cause liver damage in clinical trials or post-marketing safety data. Liver injury is not listed as a known side effect of this prescription-only weight management injection. However, if you have existing liver disease or concerns about liver health, it's important to discuss this with your GP before starting Mounjaro, as your prescriber will assess whether it's suitable for you based on your individual health profile.
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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.
What Clinical Evidence Shows About Mounjaro and Liver Safety
The SURMOUNT clinical trials, which tested tirzepatide (the active ingredient in Mounjaro) in thousands of adults over 72 weeks, did not report liver damage or liver dysfunction as a side effect. Liver injury is not listed in the UK product information or summary of product characteristics for Mounjaro. The most common side effects reported were gastrointestinal — nausea, diarrhoea, vomiting, and constipation — rather than liver-related. Post-marketing safety monitoring has continued since Mounjaro's UK approval, and no new liver safety concerns have emerged. That said, any medication can theoretically affect liver function in rare cases, which is why prescribers may check baseline liver function before starting treatment in some patients. If you have a history of liver disease, hepatitis, or cirrhosis, your GP or specialist must be informed during your clinical assessment for Mounjaro.
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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.
Liver Health Considerations Before Starting Mounjaro
Before starting Mounjaro, your prescriber will review your full medical history, including any liver conditions. Patients with severe liver disease may not be suitable for this medication. If you have mild to moderate liver disease, your prescriber may still consider Mounjaro appropriate but will monitor you more closely. Mounjaro is a prescription-only medicine that requires a clinical assessment, meaning a licensed prescriber will evaluate your individual circumstances before issuing a prescription. Use our free BMI calculator and GLP-1 weight loss calculator above to check your current health metrics, then discuss the results and any liver health concerns with your GP or the prescriber conducting your 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 toxic to the liver?
No. Clinical trial data and post-marketing safety monitoring have not identified liver toxicity as a risk with Mounjaro. Liver damage is not a known side effect. However, your prescriber will assess your individual liver health during your clinical assessment before prescribing.
Will Mounjaro affect my liver function tests?
There is no evidence that Mounjaro significantly affects liver function. However, if you have existing liver disease, your GP may monitor your liver function tests periodically as part of standard care — this is routine practice, not specific to Mounjaro.
Can I take Mounjaro if I have fatty liver disease?
Non-alcoholic fatty liver disease (NAFLD) is common in people with obesity. Weight loss through Mounjaro may actually improve NAFLD. However, you must inform your prescriber of any liver condition during assessment. They will decide if Mounjaro is safe for your specific situation.
What should I tell my GP about liver health before starting Mounjaro?
Tell your GP if you have hepatitis, cirrhosis, liver scarring, or any history of liver disease. Also mention if you take medications that affect the liver, or if you drink alcohol regularly. Your prescriber needs this information to assess suitability.
Are there any liver-related side effects I should watch for while taking Mounjaro?
Liver injury is not a documented side effect of Mounjaro. However, seek urgent medical attention if you experience persistent stomach pain, yellowing of the skin or eyes, dark urine, or severe fatigue — these can indicate liver problems unrelated to Mounjaro, but require immediate medical review.
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.