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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Mounjaro and Gallbladder Health — What UK Patients Should Know
Gallbladder problems are a potential concern with Mounjaro (tirzepatide), a prescription weight loss injection licensed in the UK. gradual weight management can increase the risk of gallstones, and Mounjaro's effect on how your stomach empties food may contribute to this risk. Understanding these potential effects and knowing when to seek medical advice is essential for anyone considering or using this medication. Your GP can provide personalised guidance based on 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/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.
Gallbladder Risk and Mounjaro — What the Evidence Shows
Gallbladder complications are listed as a possible side effect of Mounjaro in UK prescribing information. The risk comes from two mechanisms: gradual weight management itself increases gallstone formation regardless of medication, and delayed gastric emptying (how slowly Mounjaro makes food leave your stomach) may affect bile flow and gallbladder function.
- Gallstones are more common during gradual weight management (more than 1.5 kg per week)
- NHS guidance recommends slower, sustainable weight loss of 0.5–1 kg per week to minimise gallbladder risk
- Mounjaro dose titration (gradual increases) may help reduce the speed of weight loss
- Pre-existing gallbladder disease or gallstones are a contraindication — Mounjaro may not be suitable if you have these
- Some people using Mounjaro experience upper abdominal pain; this should always be reported to your GP immediately
Clinical trials of tirzepatide monitored for gallbladder events, and they were reported but are relatively uncommon. Individual risk varies based on your age, genetics, diet, and existing health conditions.
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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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When to Seek Medical Advice — Gallbladder Warning Signs
Stop taking Mounjaro and contact your GP urgently if you experience sudden severe pain in the upper right abdomen or upper centre of your stomach, especially if it spreads to your back or right shoulder. Other warning signs include persistent nausea or vomiting, yellowing of skin or eyes, dark urine, or pale stools — these may indicate gallbladder or pancreatic problems.
Before starting Mounjaro, inform your prescriber if you have a history of gallstones, gallbladder disease, or pancreatitis. Your GP can assess whether this medication is suitable for you and discuss alternatives if needed. Using our free GLP-1 weight loss calculator can help you understand projected weight loss rates at different doses, which may inform discussions about gallbladder risk with your healthcare team.
- 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 gallstones?
Mounjaro itself doesn't directly cause gallstones, but gradual weight management — which Mounjaro facilitates — increases gallstone risk. Slower weight loss (0.5–1 kg per week) is safer. If you have existing gallbladder disease, Mounjaro may not be suitable. Always discuss your gallbladder health with your GP before starting.
What are the signs of gallbladder problems with Mounjaro?
Seek urgent medical attention if you experience sudden severe upper right abdominal pain (especially radiating to the back), persistent nausea, vomiting, yellowing of skin or eyes, or pale stools. These may indicate gallbladder or pancreatic complications requiring immediate assessment.
Is Mounjaro safe if I have a history of gallstones?
If you have had gallstones or gallbladder disease, inform your prescriber before using Mounjaro. It may be contraindicated, meaning unsuitable for you. Your GP can discuss whether alternative weight loss approaches might be safer based on your medical history.
How does Mounjaro affect the gallbladder?
Mounjaro slows gastric emptying (how food leaves your stomach), which may affect bile flow and gallbladder function. Combined with gradual weight management, this increases gallstone risk. NHS guidance recommends gradual dose titration to minimise this effect.
What should I do if I develop gallbladder pain while taking Mounjaro?
Contact your GP immediately or attend A&E if pain is severe. Do not continue Mounjaro without medical guidance. Your GP may order ultrasound imaging to check for gallstones or gallbladder inflammation and will advise whether you should stop the medication.
Ready to take control of your weight loss journey?
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