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
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Can Mounjaro Cause Liver Damage?
Mounjaro (tirzepatide) is a prescription-only weight management injection, and like all medications, concerns about potential side effects are valid. The short answer: liver damage is not a known or expected side effect of Mounjaro based on clinical trial evidence. However, it's important to understand what monitoring is recommended, who should avoid it, and what to watch for. This guide explains the liver safety profile of tirzepatide and what the evidence shows for UK patients considering or using this medication.
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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 Clinical Evidence Shows About Mounjaro and Liver Safety
Clinical trials of Mounjaro (tirzepatide) did not identify liver damage as a side effect in participants. The SURMOUNT-1 trial, which followed over 2,500 adults for 72 weeks, did not report hepatic (liver) adverse events as a concern. Liver function tests were monitored during trials, and no significant liver injury was observed.
However, it's important to note that tirzepatide does affect how your body processes and stores fat, including in the liver. Some patients may experience changes in liver fat content during weight loss — which is actually expected and generally positive as weight reduces. This is different from drug-induced liver damage.
The European Medicines Agency (EMA) and UK MHRA have approved Mounjaro for weight management without specific liver safety warnings. Liver damage is not listed as a known side effect in the patient information leaflet.
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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.
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Who Needs Liver Monitoring and When Should You Contact Your GP?
If you have existing liver disease — such as cirrhosis, hepatitis, or fatty liver disease — your GP or prescriber should be aware before you start Mounjaro. Whilst clinical evidence does not show direct liver toxicity, individual assessment is important. Your prescriber may recommend baseline liver function tests before starting the medication.
You should contact your GP urgently if you experience: yellowing of skin or eyes (jaundice), unexplained dark urine, pale stools, severe stomach or upper right abdominal pain, or persistent nausea and vomiting. These could indicate liver problems, though they are rare with Mounjaro.
Regular health check-ups with your GP during Mounjaro treatment support overall safety monitoring.
Weight loss itself can improve liver health in overweight and obese individuals, especially those with non-alcoholic fatty liver disease (NAFLD). As you lose weight with Mounjaro and lifestyle changes, liver fat content typically decreases, which is a positive health outcome.
If you're concerned about liver health whilst taking Mounjaro, discuss this with your GP or the prescriber who initiated your treatment. They can arrange liver function tests if clinically indicated and advise whether Mounjaro remains appropriate for you. Always report any unusual symptoms and take Mounjaro exactly as prescribed — do not adjust doses without professional guidance.
- 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.
Does Mounjaro cause liver damage?
No. Clinical trials did not identify liver damage as a side effect of Mounjaro (tirzepatide). The SURMOUNT-1 trial monitored liver function in over 2,500 participants with no significant liver injury observed. Liver damage is not listed as a known side effect by the UK MHRA or in the patient information leaflet.
Can Mounjaro affect liver fat?
Yes, but positively. Mounjaro helps weight loss, and as you lose weight, liver fat content typically decreases — especially important if you have non-alcoholic fatty liver disease (NAFLD). This is a beneficial health outcome, not drug-induced damage.
What if I have existing liver disease — can I take Mounjaro?
If you have cirrhosis, hepatitis, or fatty liver disease, inform your prescriber before starting Mounjaro. Whilst there is no evidence of direct liver toxicity, individual assessment is essential. Your GP may recommend baseline liver function tests and continued monitoring.
What liver symptoms should prompt me to contact my GP?
Seek urgent medical advice if you experience yellowing of skin or eyes, dark urine, pale stools, severe upper right abdominal pain, or persistent nausea and vomiting — though these are rare with Mounjaro. Contact your GP if you have any concerns about symptoms during treatment.
How does Mounjaro compare to Wegovy regarding liver safety?
Both Mounjaro (tirzepatide) and Wegovy (semaglutide) are well-tolerated with no established liver damage risk in clinical evidence. Mounjaro uses a dual GIP/GLP-1 mechanism compared to Wegovy's GLP-1-only action, but neither shows liver toxicity as a known concern. Your prescriber can advise which is suitable for you based on your health profile.
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