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 Diarrhoea And Sulphur Burps: Understanding UK Access And Cost
Diarrhoea and sulphur burps are among the most commonly reported side effects of Mounjaro (tirzepatide) in the UK. These digestive symptoms affect many people starting this prescription weight management injection, particularly during the dose titration phase. Understanding what to expect, how long these effects typically last, and what your access options are—whether through NHS specialist services or private prescription—can help you make an informed decision about whether Mounjaro is right for you.
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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.
Private Prescription Costs And NHS Access Pathways
In the UK, accessing Mounjaro depends on your route: NHS specialist weight management services or private online prescription.
Private route costs: Mounjaro typically costs between £150–£300 per month depending on your dose. Costs are higher at maintenance doses (15 mg) compared to starting doses (2.5 mg). A standard KwikPen contains four weeks' doses, so monthly costs reflect the dose you're taking.
NHS route: Mounjaro is available through NHS tier 3 specialist weight management services following NICE approval. However, access varies significantly by region. Your GP can refer you to your local specialist service, though waiting lists can be lengthy in many areas. When prescribed via NHS, there is no cost to you beyond your standard prescription fee (£9.90 in England as of 2024).
Eligibility: Both routes require BMI ≥30, or BMI 27–29.9 with weight-related health conditions. Your prescriber will assess whether side effects like diarrhoea are manageable for you personally.
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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.
Managing Side Effects And What To Expect During Treatment
Diarrhoea affects up to 1 in 10 Mounjaro users; sulphur burps (belching with an unpleasant smell) are very common early on. Both typically improve as your body adjusts, usually within 4–8 weeks. Practical steps: Stay hydrated, eat smaller meals, avoid fatty or greasy foods, and increase fibre gradually. Using our free GLP-1 weight loss calculator can help you understand expected weight loss outcomes against these temporary side effects. If symptoms are severe or persistent, your prescriber can adjust your dose or medication choice. Always discuss ongoing side effects with your GP or the prescriber who issued your prescription, especially if they affect your quality of life or ability to continue treatment.
- 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.
How long do sulphur burps last on Mounjaro?
Sulphur burps are very common in the first 2–4 weeks of starting Mounjaro or after dose increases. Most users report they improve significantly within 4–8 weeks as the body adjusts. If they persist beyond 12 weeks, discuss this with your prescriber, as it may indicate the need to adjust your dose or explore alternative medications.
Can diarrhoea on Mounjaro be managed without stopping treatment?
Yes. Most diarrhoea is mild to moderate and improves with time. Practical steps include staying hydrated, eating smaller meals, limiting fatty foods, and increasing fibre gradually. Anti-diarrhoeal medication like loperamide may help but check with your GP first. If symptoms are severe, your prescriber can lower your dose or explore other options.
Is Mounjaro available on the NHS in the UK?
Yes, following NICE approval, Mounjaro (tirzepatide) is available through NHS tier 3 specialist weight management services. Access varies by region and waiting lists can be long. Your GP can refer you. Alternatively, private prescription routes are available through online consultation with UK-licensed prescribers, typically costing £150–£300 per month depending on dose.
What's the difference between NHS and private Mounjaro costs in the UK?
NHS prescriptions cost £9.90 per item in England (2024) regardless of dose. Private prescriptions cost £150–£300 per month depending on your Mounjaro dose. Private access is faster but costs more. NHS access requires referral to specialist services and may involve waiting lists, but has no medication cost beyond the standard prescription fee.
Should I switch to Wegovy if I get bad sulphur burps on Mounjaro?
Possibly. Mounjaro is a dual GIP/GLP-1 agonist; Wegovy (semaglutide) is GLP-1 only. Some users report fewer digestive side effects with GLP-1 alone, though experiences vary widely. Any switch between medications must be managed by your prescriber based on your individual health. Discuss persistent side effects with them before making changes.
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.