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 Gallstones?
Yes, gallstones are a potential side effect of Mounjaro (tirzepatide). Gallbladder problems were observed in clinical trials, though they are not common. If you're considering Mounjaro for weight management in the UK, it's important to understand this risk, recognise warning symptoms, and know when to contact your GP. This guide explains what the NHS says about gallstone risk with GLP-1 and dual receptor agonist medications like Mounjaro, and what you should monitor during treatment.
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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.
Gallstones and Mounjaro — What the Evidence Shows
Gallstone formation (cholelithiasis) is listed in the Mounjaro product information as an uncommon side effect, meaning it may affect up to 1 in 100 people. gradual weight management itself can increase gallstone risk — a known phenomenon in any weight loss scenario — but Mounjaro may further increase this risk through its effects on bile composition and gallbladder function.
In clinical trials, including the SURMOUNT studies, gallbladder-related problems were reported in participants taking tirzepatide. The NHS and MHRA monitor this risk as part of tirzepatide's additional monitoring status (Black Triangle ▼). If you have a personal or family history of gallbladder disease, your GP or prescriber should assess whether Mounjaro is suitable for you.
- Risk factors that increase gallstone likelihood: gradual weight management, female sex, family history, older age, high cholesterol
- Mounjaro dose titration from 2.5 mg up to 15 mg occurs over weeks — slower escalation may lower acute gallstone risk
- Regular monitoring and symptom awareness are important during treatment
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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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Gallstone Symptoms — When to Contact Your GP
Severe, persistent pain in the upper right stomach area (or upper centre abdomen) spreading towards the back is the main warning sign of gallstones or gallbladder inflammation. Other symptoms include nausea, vomiting, and pain that worsens after eating fatty foods. Contact your GP urgently if you experience these symptoms whilst taking Mounjaro.
The NHS advises that any acute abdominal pain whilst on weight loss medication should be assessed promptly — not all abdominal pain is gallbladder-related, but it must be evaluated. Your prescriber needs to know about any new or worsening symptoms so they can determine whether Mounjaro should be continued, paused, or stopped. Keep a symptom diary if helpful, and use our free progress tracker to log any health changes alongside your weight.
- 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 gallstone risk higher with Mounjaro than with Wegovy?
Mounjaro and Wegovy are both GLP-1 class medications (Mounjaro is a dual GIP/GLP-1 agonist) and both carry similar gallstone risk. Direct clinical comparison data is limited, but the mechanism — gradual weight management affecting bile — applies to both. Your risk profile depends more on personal factors like age, sex, and weight loss speed than on the specific medication.
Can I prevent gallstones whilst taking Mounjaro?
There is no assured prevention, but certain steps may help reduce risk: avoid very gradual weight management (NHS recommends 0.5–1 kg per week), stay hydrated, eat regular meals rather than skipping meals, and maintain adequate fat intake in your diet. Your GP can advise on personalised risk reduction based on your health history.
What happens if I develop gallstones whilst on Mounjaro?
If you develop confirmed gallstones, your prescriber will discuss whether to continue, pause, or stop Mounjaro. Some people can safely continue treatment with careful monitoring; others may need to stop. If you require gallbladder surgery, your medical team will coordinate with the prescriber managing your Mounjaro. Never stop Mounjaro abruptly without guidance.
Will my NHS GP prescribe Mounjaro if I have gallbladder disease history?
NHS tier 3 specialist weight management services assess individual risk factors before prescribing any weight loss medication. A history of gallstones does not automatically exclude you from Mounjaro, but it requires careful evaluation and informed consent. Discuss your full medical history with the specialist team.
How is Mounjaro monitored in the NHS for gallbladder safety?
The MHRA monitors tirzepatide through its Black Triangle (▼) additional monitoring scheme. Your prescriber will take a baseline history and ask about symptoms at follow-up appointments. If you develop symptoms, imaging (ultrasound) can confirm gallstones. Report all new symptoms to your GP or prescribing service promptly.
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