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 vs Wegovy — Urinary Side Effects Comparison
Urinary side effects are not commonly reported with either Mounjaro (tirzepatide) or Wegovy (semaglutide) in clinical trials. Both are GLP-1 receptor agonists licensed for weight management in UK adults — Mounjaro is a dual GIP and GLP-1 agonist, whilst Wegovy activates GLP-1 only. Understanding how these medications work and their actual side effect profiles can help you make an informed decision alongside your GP or prescriber. Individual experiences vary significantly, and clinical assessment is essential before either prescription-only medication is recommended.
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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.
Clinical Trial Data — SURMOUNT vs STEP
Mounjaro (tirzepatide) was evaluated in the SURMOUNT clinical trials, where the most frequently reported side effects were gastrointestinal: nausea, diarrhoea, vomiting, and constipation. Urinary side effects were not listed as common or very common adverse events.
Wegovy (semaglutide) was evaluated in the STEP trials with a similar side effect profile — predominantly gastrointestinal symptoms. Urinary complications or urinary tract issues were not identified as expected side effects in the trial data.
- Both medications slow gastric emptying, affecting digestion rather than urinary function
- GLP-1 activation works primarily on appetite and blood sugar regulation
- Tirzepatide's additional GIP pathway does not target the urinary system
- If urinary symptoms occur during treatment, they may be unrelated to the medication and warrant GP assessment
Neither the SURMOUNT nor STEP trial data suggests urinary side effects are a characteristic risk of these weight management injections.
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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.
Free Weight Loss Tools & Guides
Everything you need to understand your weight, explore medication options, and track your progress — completely free.
Individual Suitability and Prescriber Assessment
Both Mounjaro and Wegovy require a clinical assessment before prescription to ensure suitability for your individual health. Your prescriber will review your medical history, current medications, and any pre-existing conditions — including urinary or kidney health.
If you have a history of urinary tract infections, kidney disease, or urinary concerns, inform your GP or online prescriber during your consultation. Certain health conditions may affect medication choice or suitability.
- Neither medication is contraindicated based on urinary side effects alone
- Dehydration during GLP-1 therapy can sometimes contribute to urinary issues — maintaining fluid intake is recommended
- Any new or unusual urinary symptoms during treatment should be reported to your GP promptly
Use our free GLP-1 weight loss calculator to understand potential weight loss outcomes, and discuss your specific health profile with your prescriber for personalised guidance.
- 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.
Do Mounjaro or Wegovy cause urinary side effects?
Urinary side effects are not listed as common adverse events in either the SURMOUNT (Mounjaro) or STEP (Wegovy) clinical trials. Both medications primarily affect the gastrointestinal system. If urinary symptoms occur, discuss them with your GP — they may be unrelated to the medication.
What are the actual common side effects of these weight management injections?
The most frequently reported side effects for both Mounjaro and Wegovy are gastrointestinal: nausea, diarrhoea, vomiting, constipation, and abdominal pain. These typically improve over time as your body adjusts. Injection site reactions and fatigue are also common.
Which has fewer side effects — Mounjaro or Wegovy?
Both have similar common side effect profiles. Mounjaro's dual GIP and GLP-1 mechanism does not result in significantly different or more severe side effects than Wegovy's GLP-1-only mechanism. Individual tolerance varies — some people experience more or fewer side effects regardless of which medication is used.
Should I mention urinary concerns before starting Mounjaro or Wegovy?
Yes. Always disclose your complete medical history, including any urinary tract infections, kidney disease, or urinary symptoms, during your clinical assessment. This helps your prescriber make the best choice for you and monitor your health throughout treatment.
Can dehydration with these injections affect urinary health?
Maintaining adequate hydration is important during GLP-1 therapy. Some people experience reduced fluid intake due to decreased appetite, which can contribute to dehydration and urinary concentration. Ensure you drink enough water throughout the day — your prescriber can advise on appropriate fluid intake.
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.