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
Can Weight Loss Cause Gallstones?
Yes, gradual weight management can increase the risk of developing gallstones, particularly when losing more than 1.5 kg per week. This happens because the liver produces extra cholesterol during fast weight loss, which can crystallise in the gallbladder. However, the NHS supports gradual weight management at 0.5–1 kg per week as a safer approach. For eligible adults, prescription weight loss medication like Mounjaro and Wegovy can help achieve sustainable weight loss whilst minimising this risk. Understanding gallstone risk is important when planning your weight management journey in the UK.
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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.
Weight Loss, Gallstones, and UK Treatment Options
Gallstones form when bile contains too much cholesterol, which hardens into crystals. gradual weight management—especially crash diets or very low calorie diets (under 800 kcal per day)—increases this risk because the liver produces excess cholesterol during fast fat breakdown. The NHS recommends losing weight at a gradual rate of 0.5–1 kg per week to minimise gallstone risk whilst achieving sustainable results.
For adults with a BMI of 30 or above (or 27 or above with weight-related health conditions), prescription weight loss medication offers a safer alternative to extreme dieting. UK-licensed options include Mounjaro (tirzepatide), Wegovy (semaglutide), and Saxenda (liraglutide)—all GLP-1 or dual receptor agonists that support gradual, sustainable weight loss. Clinical trials show these medications help people lose an average of 14–21% of body weight over time, without the gallstone risk associated with crash dieting. These medications are prescription-only and require a clinical assessment from your GP or a licensed prescriber to establish eligibility and suitability.
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.
NHS Access and Finding the Right Approach for You
In the UK, you can access weight loss medication through two routes: NHS specialist weight management services (referral from your GP) or private prescribing (online consultation with a licensed prescriber). NHS access varies significantly by region and often involves waiting lists; private prescribing is typically faster. Both approaches require a clinical assessment to confirm you meet eligibility criteria and have no contraindications.
The best approach for avoiding gallstones whilst achieving weight loss is combining gradual calorie reduction with physical activity, ideally supported by medication if eligible. Use our free BMI calculator to check whether you might qualify for prescription options, and speak with your GP about the safest weight management strategy for your individual health situation. Your GP can discuss whether medication would help you lose weight sustainably without triggering gallstone formation.
- 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.
What is the connection between weight loss and gallstones?
During gradual weight management, the liver increases cholesterol production, which can crystallise in the gallbladder and form gallstones. This risk is highest when losing more than 1.5 kg per week. Gradual weight loss (0.5–1 kg weekly) and avoiding very low calorie diets significantly reduces this risk.
Which weight loss medications are available on the NHS in the UK?
Mounjaro (tirzepatide), Wegovy (semaglutide), and Saxenda (liraglutide) are all NHS-licensed for weight management in eligible adults. Access is through tier 3 specialist weight management services. Eligibility includes a BMI of 30 or above, or 27 or above with weight-related health conditions like type 2 diabetes.
How much weight can I expect to lose with prescription medication?
Clinical trials show Mounjaro helps users lose an average of 15–21% of body weight, whilst Wegovy supports loss of approximately 15% over time. However, individual results vary. These medications work best alongside reduced-calorie diet and increased physical activity.
How do I find out if I'm eligible for weight loss medication in the UK?
Speak with your GP, who can assess your BMI, health conditions, and individual circumstances. They can refer you to NHS tier 3 services if appropriate, or you can access private prescribing through an online consultation with a UK-licensed prescriber following a clinical assessment.
Can prescription weight loss medication trigger gallstones like rapid dieting can?
No. Because prescription medications support gradual, sustainable weight loss (typically 0.5–1 kg per week or slower), they carry significantly lower gallstone risk compared to crash dieting. Medication-supported weight management is actually safer for gallbladder health than extreme calorie restriction. ```
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.