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 Kidney Stones?
Kidney stones are not listed as a direct side effect of Mounjaro (tirzepatide) in clinical trials or UK prescribing data. However, any medication that affects hydration or metabolism may theoretically influence kidney stone risk. This guide explains what we know about Mounjaro safety, how it compares to Wegovy, and when to contact your GP if you have concerns about kidney health.
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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.
Mounjaro and Kidney Stone Risk — What the Evidence Shows
Clinical trial data: Kidney stones were not reported as a side effect in the SURMOUNT trials that tested Mounjaro (tirzepatide) for weight management in UK adults. The most common side effects observed were gastrointestinal—nausea, diarrhoea, constipation, and vomiting—rather than urinary or kidney-related problems.
Mechanism context: Mounjaro works as a dual GIP and GLP-1 receptor agonist, slowing gastric emptying and reducing appetite. This does not directly affect kidney function, though like any weight loss medication, adequate hydration becomes important during treatment.
- Dehydration from diarrhoea or vomiting could theoretically increase kidney stone risk in susceptible individuals
- Weight loss itself may reduce kidney stone risk in some patients
- GLP-1 medications (including Wegovy, which is a GLP-1-only agonist) do not have kidney stones as a documented side effect
If you have a personal or family history of kidney stones, inform your prescriber before starting Mounjaro.
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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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Mounjaro vs Wegovy — Kidney Safety Comparison
Both Mounjaro and Wegovy are UK-licensed prescription-only medications for weight management, and neither lists kidney stones as a direct side effect. Mounjaro is a dual GIP+GLP-1 agonist reaching a maximum dose of 15mg weekly, whilst Wegovy is a GLP-1-only agonist with a maximum dose of 2.4mg weekly. Both work through appetite regulation rather than direct effects on kidney function.
The gastrointestinal side effects common to both medications—particularly diarrhoea—emphasise the importance of staying well-hydrated during treatment. Your prescriber will assess your individual kidney health during your clinical assessment before either medication is prescribed. Our GLP-1 weight loss calculator can help you understand projected outcomes with either medication, though individual results vary significantly.
[Q1: Is dehydration from Mounjaro more likely to cause kidney stones? A1: Mounjaro itself does not cause dehydration, but gastrointestinal side effects like diarrhoea can increase fluid loss. Maintaining good hydration—typically 6–8 glasses of water daily—helps prevent kidney stone formation. If you experience persistent diarrhoea or vomiting, inform your GP or prescriber.] [Q2: Who should avoid Mounjaro due to kidney concerns? A2: Mounjaro is generally safe for people with normal kidney function. However, if you have a history of kidney stones, severe kidney disease, or kidney transplant, discuss this with your prescriber. They may recommend closer monitoring or an alternative treatment.] [Q3: Can weight loss from Mounjaro reduce kidney stone risk? A3: Yes. Research suggests excess weight increases kidney stone risk, particularly in men. Weight loss achieved through Mounjaro may reduce this risk, though individual factors like diet and hydration remain important.] [Q4: Should I drink more water whilst taking Mounjaro? A4: Yes. Staying well-hydrated is always recommended during weight loss treatment, especially if you experience diarrhoea or vomiting. Aim for at least 6–8 glasses of water daily, and more in hot weather or if you exercise regularly.] [Q5: How does Wegovy compare to Mounjaro for kidney safety? A5: Both medications have no documented kidney stone risk. Wegovy is a GLP-1-only agonist, whilst Mounjaro is dual GIP+GLP-1. Both require clinical assessment before prescription. Your GP or prescriber will consider your individual kidney health when deciding which is most suitable.]- 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 BMI and how is it calculated?
BMI (Body Mass Index) is calculated by dividing your weight in kilograms by your height in metres squared. It's the standard screening tool used by the NHS to assess whether adults are a healthy weight.
Is BMI accurate for everyone?
BMI is a useful screening tool but doesn't account for muscle mass, bone density, or body fat distribution. Athletes may have a high BMI without excess fat. The NHS recommends using BMI alongside waist circumference for a more complete picture.
What are GLP-1 medications like Mounjaro and Wegovy?
GLP-1 receptor agonists are prescription medications that mimic gut hormones to reduce appetite and help with weight loss. Mounjaro (tirzepatide) and Wegovy (semaglutide) are the two most widely used for weight management in the UK.
Am I eligible for GLP-1 weight loss medication in the UK?
Generally, you need a BMI of 30+ (obese) or 27+ with a weight-related health condition. You must be 18 or over. Use our BMI calculator to check.
What is the difference between Mounjaro and Wegovy?
Mounjaro (tirzepatide) is a dual GIP/GLP-1 agonist with up to 22.5% weight loss. Wegovy (semaglutide) is GLP-1-only with up to 15-17% weight loss. Both are weekly injections.
Is this website free to use?
Yes, 100% free. No sign-up required. All tools work instantly in your browser and no personal data is stored on our servers.
Ready to take control of your weight loss journey?
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