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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Understanding Mounjaro Sulfur Burps And Diarrhoea — UK Costs And Access
Sulfur burps and diarrhoea are among the most commonly reported side effects when starting Mounjaro (tirzepatide) treatment. These gastrointestinal effects are typically temporary and often improve as your body adjusts to the medication over the first few weeks. Understanding what to expect, how long these symptoms usually last, and whether Mounjaro is accessible and affordable in the UK can help you make an informed decision about this prescription-only weight management injection. This guide covers side effects, UK access routes, and cost information to help you navigate your options.
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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.
Mounjaro Sulfur Burps And Diarrhoea — What Causes Them And How Long They Last
Sulfur burps (also called sulphur burps or rotten egg burps) and diarrhoea are gastrointestinal side effects linked to how Mounjaro (the brand name for tirzepatide) slows gastric emptying — the rate at which food moves through your stomach. When food stays in your stomach longer, fermentation can occur, producing gas with a distinctive sulphur smell. Diarrhoea similarly results from changes in digestive speed and gut motility.
- When they occur: Usually within the first 1–2 weeks of starting Mounjaro or after a dose increase
- Duration: Most commonly last 3–7 days but can persist for 2–3 weeks in some people
- Frequency: Very common side effects — affect more than 1 in 10 people in clinical trials
- Severity: Usually mild to moderate; rarely severe enough to require stopping treatment
These side effects typically reduce significantly as your body adapts. However, they can recur when your dose increases. Speaking with your prescriber about symptom management strategies — such as dietary adjustments, hydration, and timing of doses — can help you manage these effects whilst continuing treatment.
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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.
Mounjaro In The UK — NHS And Private Access Routes
Accessing Mounjaro in the UK depends on whether you pursue the NHS route or private prescription route. Both require a clinical assessment by a UK-licensed prescriber to confirm you meet eligibility criteria (typically a BMI of 30 or above, or 27–29.9 with weight-related health conditions such as type 2 diabetes or hypertension).
- NHS access: Through tier 3 specialist weight management services via GP referral. Availability varies significantly by region; waiting times can be several months to over a year in some areas
- Private access: Through online consultations with UK-licensed prescribers, with prescription dispensed by GPhC-registered pharmacies. Available within days in most cases
- Costs: Private prescriptions typically range from £120–£280 per month depending on dose, plus the cost of the prescription itself
Many people use our GLP-1 weight loss calculator to explore projected outcomes at different Mounjaro doses before committing to 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.
What causes sulfur burps on Mounjaro?
Sulfur burps occur because Mounjaro slows gastric emptying (how quickly food leaves your stomach). Food ferments longer in your stomach, producing gas with a rotten egg smell. This is a normal physiological response and usually improves within 1–3 weeks as your body adapts to the medication.
How long do diarrhoea and sulfur burps last on Mounjaro?
Most people experience these side effects for 3–7 days after starting Mounjaro or after a dose increase. Some people report symptoms lasting 2–3 weeks. They typically resolve as your body adjusts, though they may briefly recur when your dose increases during titration.
Can I access Mounjaro through the NHS in the UK?
Yes, Mounjaro is available through NHS tier 3 specialist weight management services following a GP referral. However, access varies by region and waiting lists can be lengthy (months to over a year in some areas). Private access via online consultation is faster but involves out-of-pocket costs.
How much does Mounjaro cost on private prescription in the UK?
Private Mounjaro typically costs £120–£280 per month depending on your dose, plus the cost of the private prescription (usually £15–£50). Costs vary between providers. Starting doses are cheaper than maintenance doses. Check with multiple providers for current pricing.
Is Mounjaro the same as Wegovy?
No. Both are prescription-only weight management injections available in the UK, but Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, while Wegovy (semaglutide) is a GLP-1 agonist only. Mounjaro typically shows slightly higher average weight loss in clinical trials, but individual results vary significantly.
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.