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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Gallstones and Weight Loss in the UK
Gallstones can develop during gradual weight management, particularly with very low-calorie diets or crash dieting. If you're managing excess weight and concerned about gallstone risk, understanding safe weight loss methods and UK prescription options is important. This guide explains the link between weight loss and gallstones, explores medically-supervised weight management options available in the UK, and shows how slower, sustainable weight loss can reduce health risks. Always speak with your GP before starting any weight loss programme, especially if you have a history of gallstones.
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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.
UK Prescription Weight Loss Options for Safe Weight Management
If you're eligible for prescription weight loss support, three medications are currently licensed in the UK: Mounjaro (tirzepatide), Wegovy (semaglutide), and Saxenda (liraglutide). These GLP-1 receptor agonist medications work by reducing appetite and supporting feelings of fullness, allowing for gradual, sustainable weight loss rather than rapid reduction that increases gallstone risk.
Clinical trials show Mounjaro helps users lose an average of 15–21% of body weight, whilst Wegovy supports approximately clinically studied weight loss—alongside reduced-calorie diet and increased physical activity. Saxenda is a daily injection option for those preferring daily over weekly dosing.
- Eligibility: BMI 30 or above, or BMI 27–29.9 with weight-related health conditions (type 2 diabetes, hypertension, sleep apnoea)
- Medical supervision: These are prescription-only medicines requiring clinical assessment
- Gradual approach: Slow, managed weight loss reduces gallstone complications compared to rapid dieting
Use our free GLP-1 weight loss calculator to explore potential outcomes at different doses, and our BMI calculator to check your current health weight category.
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 Weight Loss Support: NHS vs Private Routes
In the UK, prescription weight loss medication is available through two routes. NHS access is through specialist tier 3 weight management services—typically following GP referral—though waiting lists vary significantly by region and availability can be limited. Private access is through online prescribing services where a UK-licensed prescriber assesses your eligibility following an online consultation, with prescription dispensed by a GPhC-registered pharmacy.
Whichever route you choose, medically-supervised weight loss is safer than crash dieting, particularly if gallstones are a concern. Your prescriber will monitor your progress and adjust treatment as needed. Start by speaking with your GP about your weight loss goals and any health risks, including gallstone history. They can advise on NHS tier 3 services in your area or discuss private options. Track your weight loss journey using our free progress tracker to monitor sustainable results.
- 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 weight loss cause gallstones?
Yes, gradual weight management—particularly losing more than 1.5 kg per week or following very low-calorie diets—increases gallstone risk. Slower, gradual weight loss (0.5–1 kg per week) is safer. Prescription weight loss medications support steady weight loss rather than rapid reduction, reducing this risk.
What is the safest rate of weight loss?
The NHS recommends losing 0.5–1 kg per week for sustainable, safer results. This pace reduces gallstone risk and helps preserve muscle mass. Prescription medications like Mounjaro and Wegovy are designed to support this gradual approach alongside diet and exercise changes.
Am I eligible for prescription weight loss medication on the NHS?
NHS eligibility typically requires a BMI of 30 or above, or 27–29.9 with weight-related health conditions. You'll need referral to a specialist tier 3 weight management service through your GP. Availability and waiting times vary by region and ICB funding.
What is the difference between Mounjaro and Wegovy for weight loss?
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, whilst Wegovy (semaglutide) is a GLP-1 agonist only. Mounjaro showed slightly higher average weight loss (15–21% vs 14.9%) in clinical trials. Both are once-weekly injections requiring prescription and clinical assessment.
Should I speak to my GP before starting weight loss medication if I have gallstones?
Yes, absolutely. If you have a history of gallstones or gallbladder disease, your GP must assess you before prescription medication. They'll consider your medical history, monitor your weight loss rate, and ensure it's medically safe. Never start any weight loss programme without professional guidance. ```
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.