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 Cause Gallstones?
Mounjaro (tirzepatide) is a prescription-only weight management injection licensed in the UK. Some people taking this medication have reported gallbladder problems, including gallstones. However, gallstone risk is complex and linked to gradual weight management itself, not just the medication. This guide explains what the evidence shows, warning signs to watch for, and when to contact your GP.
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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 Evidence Shows About Mounjaro and Gallstones
Gallstones can occur during gradual weight management from any cause — whether from dieting, bariatric surgery, or weight loss medication. When you lose weight quickly, your gallbladder contracts more frequently to help digest fat, which increases gallstone risk. In clinical trials of Mounjaro (tirzepatide), gallbladder problems were reported, but at relatively low rates. The SURMOUNT clinical trials did not identify gallstones as a major safety concern compared to placebo, though individual cases have been reported in real-world use. Your prescriber will assess your gallbladder health history before starting Mounjaro and monitor you during treatment. If you have a history of gallstones, previous gallbladder removal, or cholecystitis, inform your prescriber — you may not be eligible for this medication.
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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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Signs of Gallbladder Problems and When to Seek Help
Seek urgent medical attention if you experience severe pain in the upper right part of your abdomen, especially pain that spreads to your back or shoulder. Other warning signs include sudden nausea, vomiting, yellowing of the skin or eyes (jaundice), or pale, clay-coloured stools. These symptoms can indicate gallstones, inflammation, or other serious gallbladder conditions. Contact your GP immediately if you notice these signs while taking Mounjaro, or call 111 for urgent advice outside surgery hours. Do not wait for your next appointment — gallbladder problems require prompt evaluation.
- 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 directly causing gallstones or is it the weight loss?
Both factors may play a role. gradual weight management itself increases gallstone risk regardless of the cause. Mounjaro enables quick weight loss, which triggers the risk. Some gallbladder issues reported in clinical trials may also be directly related to how tirzepatide affects digestion and bile flow, though this is still being studied.
What should I tell my GP before starting Mounjaro?
Tell your prescriber immediately if you have any history of gallstones, gallbladder removal, cholecystitis, or other gallbladder disease. You should also mention any digestive conditions like pancreatitis. Your GP or licensed prescriber will assess whether Mounjaro is safe for you based on your individual health history.
Can I prevent gallstones while taking Mounjaro?
Losing weight more gradually may reduce risk, though Mounjaro's mechanism encourages relatively quick loss. Ensure adequate fat intake in your diet — very low-fat diets increase gallstone risk. Stay well-hydrated and follow your prescriber's guidance on dose titration. These steps may help but cannot eliminate risk entirely.
How is Mounjaro different from Wegovy when it comes to gallstone risk?
Both Mounjaro (tirzepatide) and Wegovy (semaglutide) are GLP-1-based medications that enable gradual weight management, so gallstone risk is similar with both. Mounjaro is a dual GIP/GLP-1 agonist while Wegovy is GLP-1 only, but both have reported gallbladder complications at similar rates in clinical practice.
What happens if I develop gallstones while on Mounjaro?
If gallstones are confirmed by ultrasound, your prescriber may recommend stopping Mounjaro. Some patients continue under close monitoring; others switch to a slower weight loss approach. Gallstone treatment depends on symptoms — your GP may recommend dietary changes, medication, or in some cases, surgical removal. Always follow your healthcare provider's advice.
Ready to take control of your weight loss journey?
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