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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Mounjaro And Kidney Pain: What You Need To Know
Kidney pain is not listed as a common side effect of Mounjaro in UK clinical trials, though some GLP-1 receptor agonists like Wegovy carry theoretical kidney considerations at very high doses. Both Mounjaro (tirzepatide) and Wegovy (semaglutide) are prescription-only medicines requiring clinical assessment before use. If you experience any abdominal or flank pain whilst taking either medication, you should contact your GP immediately, as this could indicate pancreatitis or another condition requiring urgent evaluation. Individual suitability depends on your personal health profile, kidney function, and medical history—your prescriber will assess this during your clinical assessment.
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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.
How Mounjaro And Wegovy Work: Clinical Evidence
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist—meaning it activates two hormone pathways simultaneously, which is distinct from Wegovy's single GLP-1 mechanism. In the SURMOUNT-1 clinical trial, Mounjaro showed average weight loss of 15–21% of body weight depending on dose, with no significant kidney concerns reported in trial participants with normal baseline kidney function. Wegovy (semaglutide) is a GLP-1-only agonist, showing average weight loss of approximately 15% in the STEP-1 trial. Both medications slow gastric emptying and reduce appetite through established hormone pathways. Neither medication is insulin and neither directly affects kidney function in patients with normal baseline renal health. Both are available via UK prescription following clinical assessment through NHS specialist services or private prescribers. Your GP or prescriber will review your kidney function (through blood tests measuring creatinine and eGFR) before prescribing either medication.
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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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Kidney Safety And Individual Prescriber Assessment
Kidney pain or flank pain is not a listed common or very common side effect of either Mounjaro or Wegovy in UK product information. However, any new or severe abdominal pain during GLP-1 treatment warrants immediate GP contact, as it could indicate pancreatitis, gallbladder issues, or other conditions unrelated to kidney function. Prescribers assess kidney safety using baseline eGFR (estimated glomerular filtration rate) and creatinine levels before starting either medication. Both drugs are generally considered safe for people with mild to moderate kidney function; however, severe kidney disease requires specialist assessment. The choice between Mounjaro and Wegovy depends on your individual health profile, weight loss goals, injection preference (once-weekly for both), and prescriber recommendation—not on kidney pain risk, as this is uncommon with either medication when used appropriately.
- 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.
Is kidney pain a known side effect of Mounjaro in the UK?
Kidney pain is not listed as a common or very common side effect of Mounjaro (tirzepatide) in UK clinical trials or product information. However, if you experience flank pain or abdominal pain whilst taking Mounjaro, contact your GP immediately, as it could indicate pancreatitis or another condition requiring medical evaluation.
Does Wegovy cause kidney problems or kidney pain?
Kidney pain is not a listed common side effect of Wegovy (semaglutide). Both Mounjaro and Wegovy are considered safe for people with normal kidney function. Your prescriber will check your kidney function with blood tests before prescribing either medication.
How do prescribers assess kidney safety before prescribing Mounjaro or Wegovy?
Before prescribing either medication, your GP or private prescriber will order blood tests measuring your creatinine level and eGFR (estimated glomerular filtration rate) to assess your baseline kidney function. This helps determine whether the medication is safe for you and at what dose.
What's the difference between Mounjaro and Wegovy in terms of kidney safety?
Both Mounjaro and Wegovy are assessed for kidney safety using the same baseline kidney function tests. Mounjaro is a dual GIP+GLP-1 agonist whilst Wegovy is GLP-1-only, but kidney safety profiles are comparable in patients with normal baseline renal function. Your prescriber will choose based on your individual health profile.
Should I worry about kidney pain if I'm on Mounjaro or Wegovy?
No—kidney pain is not an expected side effect of either medication. However, any new abdominal, flank, or back pain should be reported to your GP immediately, as it could indicate pancreatitis or another condition. Use our free BMI calculator to track your baseline health metrics before starting any weight loss medication.
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