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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Does Mounjaro Affect the Liver?
Mounjaro (tirzepatide) is a prescription-only GLP-1 and GIP receptor agonist injection used for weight management in UK adults. If you're considering this medication, you may have questions about its safety and potential effects on your liver. The good news is that liver damage is not listed as a known side effect in clinical trials or UK prescribing information. However, it's important to understand what the evidence shows and when you should speak to your GP about your individual health.
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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/mยฒ).
While BMI isn't a perfect measure โ it doesn't account for muscle mass, bone density, or fat distribution โ 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 โ 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 Evidence Shows About Mounjaro and Liver Health
Liver damage or liver injury is not reported as a side effect of Mounjaro (tirzepatide) in clinical trials or UK prescribing data. The SURMOUNT clinical trials, which tested Mounjaro at doses from 2.5 mg up to 15 mg weekly, did not identify liver problems as an adverse effect.
However, Mounjaro can affect how your body processes certain substances. Like all GLP-1 and GIP receptor agonists, Mounjaro may slow gastric emptying (how quickly food leaves your stomach), which is why some people experience nausea or digestive changes early in treatment. If you have a pre-existing liver condition โ such as non-alcoholic fatty liver disease (NAFLD), cirrhosis, or viral hepatitis โ your GP will need to assess whether Mounjaro is safe for you personally.
Weight loss itself is generally beneficial for liver health, especially in people with NAFLD. Losing weight can reduce fat accumulation in liver tissue and improve liver function tests. This means Mounjaro's weight-loss effects may actually benefit your liver health if you have weight-related liver disease.
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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 โ 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 โ completely free.
When to Tell Your GP About Your Liver
Before starting any weight-loss medication including Mounjaro, always inform your prescriber if you have or have had any liver problems. Your GP or the prescriber conducting your clinical assessment will review your medical history and may arrange blood tests to check your liver function before and during treatment.
Mounjaro does interact with some oral medications due to gastric slowdown, so your prescriber needs a full picture of your health. If you develop symptoms such as unexplained jaundice, persistent abdominal pain, dark urine, or pale stools while taking Mounjaro, contact your GP immediately โ these could indicate liver problems unrelated to the medication itself.
Use our free BMI calculator to understand your current health status, and discuss with your GP whether Mounjaro or other weight-loss approaches are right 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 โ 5mg โ 7.5mg โ 10mg โ 12.5mg โ 15mg
- GLP-1 receptor agonist
- Up to 15โ17% body weight loss (STEP trials)
- Weekly injection, 5-step dose escalation
- NHS & private prescription available
- Doses: 0.25mg โ 0.5mg โ 1mg โ 1.7mg โ 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 | 15โ22.5% | 12โ17% |
| Key trial | SURMOUNT-1 (2022) | STEP 1 (2021) |
| Max dose | 15 mg weekly | 2.4 mg weekly |
| Escalation period | 20โ32 weeks | 16โ20 weeks |
| Administration | Weekly injection (pen) | Weekly injection (pen) |
| NHS availability | Private prescription only | NHS & private |
| Approx. private cost | ยฃ150โยฃ250/month | ยฃ150โยฃ300/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 โ 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 for people with fatty liver disease?
Mounjaro is not specifically contraindicated for fatty liver disease, but requires individual assessment. In fact, weight loss from Mounjaro may help improve NAFLD. Your GP must review your case and liver function tests before prescribing. Always disclose your liver condition during your clinical assessment.
Does Mounjaro cause liver damage?
No, liver damage is not reported as a side effect of Mounjaro in clinical trials or UK prescribing information. However, pre-existing liver conditions require GP assessment before starting treatment to ensure it is safe for your individual health situation.
Will Mounjaro affect my liver function tests?
Mounjaro itself does not typically cause abnormal liver function tests. However, your GP may check liver function before starting treatment and monitor during use, especially if you have known liver disease. Weight loss from Mounjaro often improves liver health markers.
Can I take Mounjaro if I have cirrhosis?
Cirrhosis requires specialist assessment. Your GP must review your case before considering Mounjaro. Some liver conditions may make Mounjaro unsuitable, whilst others may be manageable with close monitoring. Never start Mounjaro without discussing your cirrhosis diagnosis with your prescriber.
How does tirzepatide compare to Wegovy for liver safety?
Both Mounjaro (tirzepatide) and Wegovy (semaglutide) are prescription-only weight-management medications. Neither is associated with liver damage in clinical trials. The choice between them depends on your individual health, prescriber recommendation, and clinical assessment โ liver safety profiles are similar.
Ready to take control of your weight loss journey?
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