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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Can Mounjaro Make You Sick?
Yes, Mounjaro (tirzepatide) can cause nausea and other digestive side effects in many people — but these typically improve over time. This prescription-only injection works by activating GLP-1 and GIP hormone pathways, which naturally affect your stomach and appetite signals. Most side effects are temporary and manageable, though it's important to know what to expect and when to contact your GP. The NHS recognises these effects as normal during the dose titration phase, and they often settle within the first few weeks of treatment.
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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 Side Effects and Nausea — What the NHS Says
Mounjaro commonly causes nausea, particularly when starting treatment or increasing your dose. Clinical trial data shows nausea affects more than 1 in 10 people. Other very common digestive side effects include diarrhoea, vomiting, constipation, and stomach (abdominal) pain.
- Nausea: Usually peaks in the first 1–2 weeks after a new dose, then improves significantly by week 3–4
- Vomiting: Less common than nausea but can occur, especially if you eat too quickly or too much
- Diarrhoea or constipation: Your digestive system adjusts as your Mounjaro dose increases through the titration schedule
- Stomach pain: Usually mild; severe pain spreading to your back may indicate pancreatitis (seek urgent medical attention)
- Indigestion: More common at higher doses; often improves with smaller, frequent meals
The NHS advises that these side effects are usually mild to moderate and tend to decrease over time. If nausea is severe or persists beyond 4 weeks, your GP or prescriber may recommend dose adjustment or temporary pause in escalation.
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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 Mounjaro Sickness — Practical Tips
Most people can manage Mounjaro nausea with simple lifestyle adjustments. Eat smaller, frequent meals rather than large portions — this is often the single most effective strategy. Avoid fatty, greasy, or heavily spiced foods immediately after injection, and stay well hydrated throughout the day. Some people find eating plain foods (toast, rice, crackers) helpful during the first few days after injection.
When to contact your GP: Seek medical advice if nausea persists beyond 4 weeks, prevents you eating or drinking, or if you experience severe stomach pain spreading to your back (possible pancreatitis). Your prescriber may adjust your dose or switch you to an alternative like Wegovy (semaglutide), which some people tolerate better. Use our GLP-1 weight loss calculator to explore how different medications might work for your situation.
- 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 nausea from Mounjaro permanent?
No. In most people, nausea peaks in the first 1–2 weeks after starting or increasing your dose, then improves significantly by weeks 3–4. Your body adapts to the medication, and nausea typically becomes much less bothersome. If it persists beyond 4 weeks, contact your GP — dose adjustment may help.
Can I take anti-sickness medication with Mounjaro?
You can use over-the-counter anti-nausea remedies like ginger or peppermint tea. However, do not take prescription anti-sickness medication without consulting your GP first, as some may interact with Mounjaro or affect how it works. Always ask your prescriber before adding any new medication.
What's the difference between Mounjaro nausea and Wegovy side effects?
Both medications can cause nausea, but Mounjaro (dual GIP/GLP-1 agonist) and Wegovy (GLP-1 only) work via different pathways. Clinical trials suggest similar nausea rates, but individual tolerance varies. Some people tolerate one better than the other — your prescriber can discuss switching if needed.
Should I stop Mounjaro if I feel sick?
Do not stop suddenly without medical advice. Speak to your GP or prescriber first. They may recommend temporary dose reduction, slower escalation, or dietary changes. Stopping abruptly can affect your blood sugar if you have diabetes. Always discuss concerns with your healthcare team.
How long is the Mounjaro dose titration schedule?
Mounjaro escalates over approximately 5 months: starting at 2.5 mg (weeks 1–4), then 5 mg, 7.5 mg, 10 mg, 12.5 mg, and finally 15 mg (maximum). You spend at least 4 weeks on each dose before increasing. This gradual titration helps your body adapt and reduces early nausea. Nausea during titration is very common but usually temporary.
Ready to take control of your weight loss journey?
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