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
Mounjaro, Kidney Health, and Wegovy — What You Need to Know
Both Mounjaro (tirzepatide) and Wegovy (semaglutide) are prescription-only weight loss injections licensed in the UK, and both require careful consideration if you have kidney concerns. Neither medication is recommended for people with severe kidney disease, but mild to moderate kidney function changes may not prevent use. This guide compares how both medications are monitored and what kidney health means for your eligibility. Always discuss your individual kidney status with your GP or prescriber before starting any weight loss treatment.
10,000+ calculations today · NHS-aligned thresholds · 100% free
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.
How Mounjaro and Wegovy Differ in Kidney Considerations
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist that works through two hormone pathways. Wegovy (semaglutide) is a GLP-1 receptor agonist only. Both medications are metabolised and excreted by the kidneys, which is why kidney function matters when assessing suitability. Neither drug is directly toxic to the kidneys, but both can affect blood pressure, blood sugar, and fluid balance — all factors that protect kidney health.
- Mounjaro: Tirzepatide is excreted primarily unchanged via the kidneys
- Wegovy: Semaglutide undergoes hepatic metabolism before renal excretion
- Both require baseline kidney function tests (eGFR and creatinine) before starting
- Both are contraindicated in severe kidney disease (eGFR <15 mL/min/1.73m²)
- Clinical trials excluded patients with significant kidney impairment, so real-world data in this population is limited
Use our free GLP-1 weight loss calculator to explore suitability — your prescriber will assess your kidney function alongside other health factors.
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.
Kidney Monitoring and Individual Suitability
If you have mild to moderate kidney disease, your prescriber may still offer Mounjaro or Wegovy, but you will need regular blood tests to monitor kidney function (eGFR), electrolytes, and blood pressure. Weight loss itself can improve kidney health outcomes in people with obesity and type 2 diabetes, which may offset some risk. However, gradual weight management or dehydration can temporarily reduce kidney function, so staying hydrated and losing weight gradually is essential.
Your GP or specialist prescriber will decide which medication (if any) is appropriate based on your eGFR level, blood pressure, blood sugar control, and overall health. This is a personalised clinical decision — there is no universal "kidney-safe" choice between the two. Both require prescription and 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?
Mounjaro is not recommended if you have severe kidney disease (eGFR below 15). For mild to moderate kidney impairment, your GP or prescriber may consider it, but you will need regular kidney function tests. Always tell your prescriber about any kidney problems before starting treatment.
Is Wegovy safer for kidneys than Mounjaro?
Neither medication is inherently safer for kidneys. Both require kidney monitoring. Semaglutide (Wegovy) undergoes liver metabolism first, while tirzepatide (Mounjaro) is excreted more directly via the kidneys. Your individual kidney function and other health factors determine suitability — this is a prescriber decision based on clinical assessment, not a choice between them.
What kidney tests do I need before starting these injections?
You will need a baseline blood test to measure eGFR (estimated glomerular filtration rate) and serum creatinine. Your GP or prescriber may also check electrolytes and blood pressure. These tests establish your baseline kidney function. Repeat tests will be scheduled during treatment depending on your baseline results and prescriber recommendations.
Can weight loss improve kidney health?
Yes — losing weight can improve kidney function outcomes in people with obesity, especially those with type 2 diabetes or high blood pressure. However, gradual weight management or dehydration can temporarily worsen kidney function. Gradual, steady weight loss (around 0.5–1 kg per week) and staying well-hydrated offer the best protection for kidney health during treatment.
What happens if my kidney function changes during treatment?
Your prescriber will adjust or stop treatment if kidney function declines significantly. Regular monitoring means any changes are detected early. Do not stop treatment without medical guidance. Always report symptoms like reduced urination, unusual thirst, or fatigue to your GP or prescriber immediately.
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.