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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Being Sick on Mounjaro — Managing Nausea and Vomiting
Nausea and vomiting are common side effects when starting Mounjaro (tirzepatide), affecting many UK adults on this weight management injection. These symptoms typically appear in the first few weeks as your body adjusts to the medication, but understanding how to manage them and when to seek help from your GP can make a real difference. This guide explains what to expect, practical strategies to reduce nausea, and when medical support is needed according to NHS guidance.
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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 in the UK?
Nausea is one of the most frequently reported side effects of Mounjaro in clinical trials, affecting up to 1 in 3 people starting the medication. Vomiting is less common but still occurs in a significant number of users. These symptoms are generally mild to moderate and tend to improve as your body adjusts over 2–4 weeks, though some people experience them for longer.
Nausea typically peaks during the dose titration phase — as your Mounjaro dose increases from 2.5 mg through to the maintenance dose. Once you reach a stable dose, many people find symptoms improve substantially. Your prescriber will monitor how you're managing and can adjust your dose schedule or provide additional support if needed. It's important to distinguish between normal adjustment nausea and more serious symptoms that require urgent attention from your GP.
- Mild nausea may pass with simple strategies like eating smaller meals and staying hydrated
- Persistent vomiting lasting more than a few hours needs GP attention
- Any vomiting with severe stomach pain requires urgent medical assessment
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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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Practical Strategies to Manage Nausea While on Mounjaro
Dietary changes are often the most effective first step. Eating smaller, more frequent meals instead of three large ones, avoiding fatty or spicy foods, and staying well hydrated with water and electrolyte drinks can significantly reduce nausea. Many people find that eating slowly and chewing thoroughly helps their digestive system cope better with Mounjaro's effects.
If nausea is affecting your daily life, speak to your GP or prescriber — they may recommend anti-nausea medication (such as metoclopramide), adjusting your injection timing, or temporarily pausing dose increases. Some people benefit from ginger supplements or acupressure wristbands, though discuss these with your healthcare provider first. Never stop taking Mounjaro without guidance. Keep a symptom diary to track patterns — this helps your GP understand what's triggering your nausea and adjust your management plan accordingly.
- 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 feeling sick on Mounjaro normal and will it pass?
Yes, nausea affects up to 1 in 3 people starting Mounjaro and is a very common adjustment symptom. For most people, it improves within 2–4 weeks as the body adapts. However, everyone's experience is different, and some people experience nausea longer. Your GP can help manage symptoms during this adjustment period.
What's the difference between normal nausea and a serious side effect?
Normal adjustment nausea is mild to moderate, occurs without severe pain, and improves with dietary changes and time. Serious warning signs include severe persistent vomiting lasting hours, vomiting with severe stomach pain (possible pancreatitis), or vomiting accompanied by fever or yellowing of skin. These require urgent GP assessment.
Can my GP prescribe anti-nausea medication alongside Mounjaro?
Yes. If dietary strategies and time don't resolve nausea, your GP or prescriber can recommend anti-nausea medication to help manage symptoms while your body adjusts. Common options in the UK include metoclopramide or ondansetron. Always inform your prescriber of any new medications you're taking.
Should I stop taking Mounjaro if I feel sick?
Never stop Mounjaro without guidance from your prescriber, even if you feel very sick. Instead, contact your GP immediately. They may adjust your dose, slow your dose increase, suggest anti-nausea support, or recommend temporary pausing. Stopping suddenly without medical advice isn't safe.
How does Mounjaro's dose titration affect nausea?
Nausea often peaks during dose increases — when moving from 2.5 mg to 5 mg, 5 mg to 7.5 mg, and so on. Some people find staying on a lower dose longer helps. Your prescriber can adjust your titration schedule based on how you're managing. Using our GLP-1 weight loss calculator can help you understand what different doses mean for your health.
Ready to take control of your weight loss journey?
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