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 Sickness and Nausea
Nausea and sickness are very common side effects when starting Mounjaro (tirzepatide), affecting more than 1 in 10 people in clinical trials. These symptoms typically occur during dose escalation and often improve over time as your body adjusts. Understanding what to expect, how to manage symptoms, and when to contact your GP can help you navigate this aspect of treatment. This guide covers everything you need to know about Mounjaro-related sickness in the UK context.
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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 Common Is Sickness on Mounjaro?
Nausea is one of the most frequently reported side effects of Mounjaro. According to SURMOUNT clinical trial data, nausea affects more than 1 in 10 people taking tirzepatide. The risk and severity of nausea typically increase when you move to a higher dose — most commonly during the first week after a dose escalation.
- Very common (more than 1 in 10): Nausea
- Very common (more than 1 in 10): Vomiting
- Very common (more than 1 in 10): Diarrhoea and constipation
Most people who experience nausea find it settles within the first few days after a dose increase. Your body gradually adapts to the medication as your dose remains stable. If sickness persists or is severe, your prescriber may recommend strategies to manage symptoms or discuss whether to continue at your current dose or pause escalation temporarily.
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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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Managing Mounjaro-Related Sickness
Several practical strategies can help reduce nausea when taking Mounjaro. Eating small, frequent meals rather than large portions is often helpful — the medication naturally reduces appetite, so smaller meals align better with how you feel. Avoid fatty, greasy, or heavily spiced foods, which can trigger nausea. Stay well hydrated by sipping water throughout the day. Ginger tea or ginger supplements may help some people, though always check with your GP before adding supplements.
If nausea is affecting your ability to eat enough or stay hydrated, contact your prescriber. They may recommend pausing dose escalation, adjusting your diet, or in some cases, temporarily stopping Mounjaro. Never adjust your dose yourself — always speak to your prescriber first. Track your symptoms using our free progress tracker to help identify patterns and share with your healthcare team.
- 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 does Mounjaro nausea last?
Most people experience nausea for the first few days after a dose increase, typically settling within 3–7 days. If nausea persists beyond a week or is severe, contact your GP. Each person's body adjusts differently, but nausea tends to improve significantly after 1–2 weeks at a stable dose.
Is feeling sick on Mounjaro normal?
Yes, nausea is a very common side effect affecting more than 1 in 10 people in clinical trials. It is expected, especially during dose escalation, but it should improve as your body adjusts. If you're concerned, always speak to your prescriber.
What should I eat if Mounjaro makes me feel sick?
Eat small, frequent meals with bland, light foods. Avoid fatty, greasy, or spiced foods. Try ginger tea, plain rice, toast, or protein smoothies. Stay hydrated by sipping water. Because Mounjaro reduces appetite, smaller meals often feel more manageable and cause less nausea.
When should I contact my GP about Mounjaro sickness?
Contact your GP if nausea is severe, lasts more than a week, prevents you from eating or staying hydrated, or if you're vomiting frequently. You should also seek urgent care if you experience severe stomach pain spreading to your back, which could indicate pancreatitis.
Can my prescriber help if Mounjaro makes me too sick?
Yes. Your prescriber can suggest dietary changes, recommend staying at your current dose longer before escalating, or discuss pausing treatment temporarily. Never stop or adjust your dose alone — always contact your prescriber first for guidance on managing side effects.
Ready to take control of your weight loss journey?
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