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
Nausea is one of the most common side effects when starting Mounjaro (tirzepatide), affecting more than 1 in 10 people. The good news is that for most people, nausea tends to improve within the first few weeks as your body adjusts to the medication. Understanding why it happens and knowing how to manage it can make a real difference to your experience. This guide explains what to expect, when to contact your GP, and practical steps you can take to feel better while on this prescription weight management injection.
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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.
Why Nausea Happens on Mounjaro
Mounjaro works by activating two hormone pathways — GIP and GLP-1 receptors — that help regulate appetite and blood sugar control. One of the ways these hormones work is by slowing gastric emptying, which means food moves more slowly through your stomach. This is part of how the medication helps you feel fuller for longer, but it can also trigger nausea as your digestive system adjusts.
The nausea is typically mild to moderate and most pronounced in the first 1–2 weeks after starting Mounjaro or increasing your dose. Your GP will start you on a low dose (2.5 mg) and gradually increase it every 4 weeks, which helps your body adapt. Additionally, the Mounjaro KwikPen is designed to deliver a precise dose once weekly, and individual responses vary — some people experience minimal nausea whilst others notice it more significantly.
Important to know: nausea does not mean the medication is not working. It is simply your body adjusting to how the tirzepatide is affecting your digestive system.
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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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Practical Steps to Manage Nausea
Eat smaller, frequent meals — instead of three large meals, try five to six smaller ones throughout the day. Avoid greasy, spicy, or heavy foods, which can worsen nausea. Focus on bland, easy-to-digest options like toast, rice, pasta, and plain chicken.
Stay hydrated — sip water, herbal tea, or ginger tea throughout the day. Ginger has natural anti-nausea properties and may help.
Slow down your eating — chew food thoroughly and eat more slowly, which reduces strain on your digestive system.
Avoid triggers — identify foods or smells that make nausea worse and avoid them temporarily.
Rest after eating — avoid strenuous exercise immediately after meals.
If nausea is severe or does not improve after 2–3 weeks, contact your GP. They may recommend anti-nausea medication or discuss whether your dose needs adjustment.
- 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 nausea last when starting Mounjaro?
For most people, nausea peaks in the first 1–2 weeks and significantly improves by weeks 3–4 as your body adjusts. Some people experience mild nausea for longer, whilst others have very little. If nausea persists beyond 4 weeks at your current dose, contact your GP — they can advise whether to adjust your dose or consider other options.
Should I stop taking Mounjaro if I feel sick?
No — do not stop without speaking to your GP first. Nausea is a known side effect that typically improves with time and does not indicate the medication is harmful. However, if you feel unwell or experience severe persistent nausea, contact your GP for guidance. They may suggest dose adjustments, anti-nausea medication, or strategies to help you manage it.
Is nausea a sign that Mounjaro is working?
Not necessarily. Nausea and weight loss are independent — some people lose weight with minimal nausea, whilst others experience nausea without significant initial weight loss. The medication's effectiveness is measured over weeks and months, not by how much nausea you feel. Your GP or prescriber will monitor your progress through clinical assessment.
Can I take anti-sickness tablets with Mounjaro?
Yes — common anti-nausea medications like ondansetron (Zofran) can be used alongside Mounjaro if nausea is significant. However, always discuss this with your GP or prescriber first, as they need to know all medications you are taking. Some anti-nausea options are available over-the-counter, but prescription guidance is recommended.
Does nausea mean I need to reduce my Mounjaro dose?
Not necessarily. Most people's nausea improves naturally without dose reduction. However, if nausea is severe or affects your quality of life significantly, your GP may suggest delaying your next dose increase or temporarily staying at your current dose longer. Never adjust your dose yourself — always discuss changes with your prescriber.
Ready to take control of your weight loss journey?
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