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 Liver Enzymes?
Mounjaro (tirzepatide) is a prescription-only GLP-1 and GIP receptor agonist weight loss injection licensed in the UK. Many people starting Mounjaro ask whether it affects liver function or causes changes in liver enzymes. The short answer is: clinical trials have not shown significant liver enzyme changes in most people, though individual responses vary. Your GP or prescriber will monitor your liver function through blood tests if needed, especially if you have existing liver concerns. This guide explains what the evidence shows and what monitoring typically involves.
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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 Does the Clinical Evidence Show?
In the SURMOUNT clinical trials, which tested Mounjaro (tirzepatide) across thousands of participants, liver enzyme elevations were not a commonly reported side effect. Most people taking Mounjaro at doses up to 15 mg weekly did not experience changes in liver function tests. However, isolated cases of liver enzyme changes have been reported, and your prescriber will assess your individual risk based on your medical history, current medications, and any existing liver conditions.
If you have non-alcoholic fatty liver disease (NAFLD), type 2 diabetes, or other metabolic conditions, your prescriber may recommend baseline liver function tests before starting Mounjaro. This allows them to monitor for any changes during treatment. Weight loss itself typically improves liver health in people with fatty liver disease, so any liver enzyme benefits from weight loss with Mounjaro may outweigh potential medication-related changes.
Try our GLP-1 weight loss calculator to explore potential weight loss outcomes at different Mounjaro doses, and use our BMI calculator to understand your current metabolic health baseline.
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If your BMI suggests you're overweight or obese, explore our GLP-1 calculators to project potential weight loss on Mounjaro or Wegovy.
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Liver Monitoring During Mounjaro Treatment
If you start Mounjaro, your prescriber should assess whether liver function tests are needed before and during treatment. Standard monitoring typically involves blood tests at baseline and periodically thereafter, depending on your risk profile. You should inform your prescriber if you:
- Have a history of liver disease or hepatitis
- Have non-alcoholic fatty liver disease (NAFLD)
- Have cirrhosis or liver scarring
- Take medications that affect liver function
- Drink alcohol regularly
If liver enzyme changes are detected, your prescriber may continue Mounjaro with closer monitoring, adjust the dose, or recommend discontinuing the medication. Always report any symptoms such as yellowing of skin or eyes, dark urine, pale stools, or upper abdominal pain to your GP immediately, as these could indicate liver problems.
- 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.
Can Mounjaro cause liver damage?
Clinical trials have not identified liver damage as a common side effect of Mounjaro. However, rare cases of liver enzyme elevation have been reported. Your prescriber will assess your individual risk and may recommend liver function monitoring if you have existing liver conditions or risk factors.
Do I need liver tests before starting Mounjaro?
It depends on your medical history. If you have liver disease, fatty liver, hepatitis, or other risk factors, your prescriber will likely order baseline liver function tests. This helps establish a baseline for monitoring during treatment.
How does weight loss from Mounjaro affect liver health?
Weight loss typically improves liver health, especially in people with non-alcoholic fatty liver disease (NAFLD). The metabolic benefits of losing weight may actually help protect liver function, potentially offsetting any medication-related enzyme changes.
What should I tell my prescriber about my liver health?
Inform your prescriber if you have any history of liver disease, fatty liver disease, hepatitis, cirrhosis, or if you drink alcohol regularly. Also mention any medications you take that affect liver function, as these may interact with Mounjaro.
What liver enzyme changes count as dangerous on Mounjaro?
Significant liver enzyme elevations (typically more than 3 times the upper limit of normal) warrant closer monitoring or discontinuation. Minor elevations may be monitored. Your prescriber will interpret results in context of your health profile. Always seek urgent medical advice if you develop yellowing of skin/eyes, dark urine, or severe abdominal pain.
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