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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Does Mounjaro Affect Kidneys?
Mounjaro (tirzepatide) is a prescription-only GLP-1 and GIP receptor agonist weight loss injection used in the UK. If you're considering this medication, you may be concerned about how it affects your kidneys. The good news is that current evidence and NHS guidance do not indicate that Mounjaro directly damages healthy kidneys. However, people with existing kidney problems need careful monitoring by their prescriber before and 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.
What the Evidence Shows About Mounjaro and Kidney Function
Clinical trials and real-world data from patients using Mounjaro show no direct kidney damage in people with normal kidney function. The medication does not work on the kidneys themselves—it acts on GLP-1 and GIP receptors in the brain and gut to regulate appetite and food intake.
However, several factors require careful attention: Weight loss itself can change kidney function temporarily, and dehydration (which may occur with gastrointestinal side effects like diarrhoea and vomiting) can stress the kidneys. People with type 2 diabetes taking Mounjaro may see improvements in kidney markers as blood sugar control improves, though this varies individually. If you have pre-existing kidney disease or reduced kidney function (eGFR below 60), your GP or prescriber must assess whether Mounjaro is suitable and monitor your kidney function closely with blood tests before starting and regularly 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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NHS Monitoring and When to Seek Medical Advice
Before starting Mounjaro, your prescriber will review your full medical history and may request kidney function tests (measuring creatinine and eGFR levels). During treatment, kidney function is typically monitored through routine blood tests, especially if you have diabetes or other risk factors.
Seek urgent advice from your GP if you experience persistent nausea and vomiting, severe dehydration, unexplained weight loss beyond expectations, or changes in urination patterns while taking Mounjaro. These symptoms may indicate dehydration affecting kidney function. It's also important to drink plenty of water, maintain a balanced diet, and use our free GLP-1 weight loss calculator to track expected results and identify any unusual patterns in your weight loss trajectory.
- 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 Mounjaro cause kidney failure?
No—clinical evidence shows Mounjaro does not directly cause kidney damage or failure in people with healthy kidneys. However, severe dehydration from side effects like vomiting can stress kidneys. People with existing kidney disease need careful assessment by their prescriber before starting treatment.
Do I need kidney tests before starting Mounjaro in the UK?
Yes, your prescriber will assess your kidney function as part of the clinical assessment before prescribing. Blood tests measuring creatinine and eGFR may be requested, especially if you have diabetes, high blood pressure, or other risk factors for kidney disease.
What happens to kidney function during weight loss with Mounjaro?
Weight loss itself can cause temporary changes in kidney function markers. As your body loses fat, kidney stress may temporarily increase. However, if you have type 2 diabetes, improving blood sugar control often improves kidney function over time. Your prescriber will monitor this.
Is Mounjaro safe if I have chronic kidney disease?
It depends on the severity of your kidney disease. If you have reduced kidney function (eGFR below 60), your GP must assess whether Mounjaro is appropriate and monitor you closely with regular blood tests. Some people with mild kidney disease can use it safely with supervision.
What warning signs suggest Mounjaro is affecting my kidneys?
Seek medical advice if you experience persistent vomiting, severe dehydration, unusual changes in urination, or unexplained gradual weight management. These can indicate dehydration affecting kidney function. Regular check-ins with your GP help catch any issues early.
Ready to take control of your weight loss journey?
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