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 vs Wegovy
Both Mounjaro (tirzepatide) and Wegovy (semaglutide) are prescription-only GLP-1 receptor agonists used for weight management in the UK. Neither medication is known to directly damage kidneys in clinical trials, though both require careful monitoring in people with existing kidney disease. This guide compares kidney safety between the two medications and explains what you should know before starting treatment. Always discuss kidney health with your GP or prescriber during your clinical assessment.
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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.
Kidney Safety: Clinical Trial Evidence and Monitoring
Clinical trials for both Mounjaro and Wegovy did not show direct kidney damage in participants with normal kidney function. However, both medications are cleared by the kidneys, so monitoring is important if you have existing kidney disease.
Mounjaro (tirzepatide): The SURMOUNT trials included participants with mild to moderate kidney disease. No significant worsening of kidney function was reported, though people with severe kidney disease (eGFR <30) were excluded from trials.
Wegovy (semaglutide): The STEP trials similarly showed no direct kidney damage. Semaglutide is used safely in people with type 2 diabetes who often have mild kidney disease, though dose adjustments may apply in severe cases.
Both medications require dose adjustment or avoidance if you have severe kidney disease (eGFR <30 mL/min/1.73m²). Your prescriber will assess your kidney function through blood tests before prescribing either medication.
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If your BMI suggests you're overweight or obese, explore our GLP-1 calculators to project potential weight loss on Mounjaro or Wegovy.
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Key Differences and Individual Suitability
The main difference between the two medications is their mechanism: Mounjaro is a dual GIP and GLP-1 receptor agonist, while Wegovy is a GLP-1 agonist only. Both are cleared renally, so kidney function matters with either drug. Neither has a specific advantage for kidney safety over the other — suitability depends on your individual health profile.
If you have kidney disease or reduced kidney function, your prescriber will assess whether either medication is appropriate for you through blood tests (eGFR and creatinine). Weight loss itself may improve kidney function by reducing pressure on kidneys and lowering blood sugar and blood pressure. Your GP can explain which medication is safest for your specific situation during your clinical assessment.
- 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 kidney disease?
If you have mild to moderate kidney disease, Mounjaro may be suitable following a clinical assessment and blood tests. However, Mounjaro is not recommended if you have severe kidney disease (eGFR <30). Always inform your prescriber of any kidney problems before starting treatment.
Is Wegovy safer for kidneys than Mounjaro?
No — neither medication is proven safer for kidneys than the other. Both are cleared by the kidneys and require monitoring. Suitability depends on your individual kidney function, which your prescriber will assess through blood tests before prescribing.
What kidney tests do I need before starting Mounjaro or Wegovy?
Your prescriber will order blood tests to measure eGFR (estimated glomerular filtration rate) and creatinine levels. These show how well your kidneys are working. If your kidney function is severely reduced, neither medication may be recommended.
Can weight loss from Mounjaro or Wegovy improve kidney function?
Yes — weight loss can reduce pressure on kidneys and lower blood pressure and blood sugar, which may improve kidney function over time. This is one reason why weight management is beneficial for people with kidney disease, though medication choice must still be personalised.
Do I need kidney monitoring while taking Mounjaro or Wegovy?
If you have existing kidney disease, your GP may recommend periodic kidney function tests (blood tests) while taking either medication. If your kidney function is normal, routine monitoring is not typically needed, but inform your prescriber of any new symptoms.
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