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
Free tracker included with every download this week
Why Does Mounjaro Cause Gallstones?
Mounjaro (tirzepatide) can increase the risk of gallstone formation, though this risk is relatively uncommon. This happens because gradual weight management itself — not the medication directly — can trigger gallstone development. When you lose weight quickly, cholesterol in the bile becomes more concentrated, creating conditions where gallstones may form. Understanding this risk, knowing what symptoms to watch for, and discussing gallbladder health with your GP before starting Mounjaro is important for safe treatment.
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Calculate Your BMI Instantly
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.
How Mounjaro Affects Gallstone Risk
Gallstones are hard deposits that form in the gallbladder, typically made of cholesterol or bilirubin. Mounjaro doesn't directly cause gallstones, but gradual weight management associated with the medication can increase risk. When you lose weight quickly — particularly at rates faster than 0.5 to 1 kg per week — the liver secretes more cholesterol into bile, and the gallbladder doesn't contract as efficiently. This combination creates an environment where cholesterol crystals can accumulate and form stones.
Clinical data shows that people experiencing gradual weight management, whether through medication, surgery, or diet, have higher gallstone incidence than those losing weight slowly. In Mounjaro clinical trials, gallbladder-related events occurred in a small percentage of participants. Your individual risk depends on several factors: age, family history of gallstones, whether you have existing gallbladder disease, your baseline weight, and how quickly you lose weight on Mounjaro.
Clinically BackedWeight Loss
No appointments. No waiting rooms. Just care — from a UK-regulated online pharmacy.
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.
Free Weight Loss Tools & Guides
Everything you need to understand your weight, explore medication options, and track your progress — completely free.
Accessing Mounjaro Safely and Monitoring Gallbladder Health
Before starting Mounjaro, your prescriber should assess your gallbladder health history. If you have a personal or family history of gallstones, or have had gallbladder problems, inform your GP or online prescriber immediately. Once you start treatment, watch for warning signs: severe pain in the upper right stomach area, pain between the shoulder blades, nausea, or vomiting. If you experience these symptoms, contact your GP urgently — do not wait.
NHS access to Mounjaro involves assessment through specialist tier 3 weight management services, though availability varies by region. Private online prescribers in the UK assess medical history before issuing a prescription from a UK-licensed pharmacy. Regardless of route, use our GLP-1 weight loss calculator to understand projected outcomes, and discuss gallbladder monitoring with your healthcare provider throughout treatment.
- 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 I take Mounjaro if I have a history of gallstones?
Not without medical assessment. Inform your GP or prescriber immediately if you have ever had gallstones or gallbladder disease. They may advise against Mounjaro or recommend additional monitoring. Each case is individual — a prescriber can assess your specific risk.
What symptoms of gallstones should I watch for on Mounjaro?
Seek urgent medical advice if you experience sudden severe pain in the upper right abdomen, pain between shoulder blades, persistent nausea, vomiting, or yellowing of skin. These may indicate gallbladder problems and require immediate GP assessment.
Does slowing weight loss reduce gallstone risk?
Yes. Losing weight at a slower rate (0.5–1 kg per week) is safer for gallbladder health. Your prescriber can adjust your Mounjaro dose to support more gradual weight loss if you have gallbladder risk factors.
How is Mounjaro prescribed in the UK?
Through NHS specialist weight management services (tier 3) or via private online prescribing from a UK-licensed prescriber. Both routes require clinical assessment of your health history, including gallbladder status, before a prescription is issued.
Should I have gallbladder tests before starting Mounjaro?
Ask your GP. If you have symptoms or significant risk factors, they may recommend ultrasound screening. Most people without symptoms don't require routine testing, but those with history should discuss screening with their prescriber.
Ready to take control of your weight loss journey?
Start with a free BMI check, explore your GLP-1 options, or begin tracking your progress today. No sign-up. No cost. Just results.