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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Mounjaro Nausea and Sickness — What You Need to Know
Nausea and sickness are among the most commonly reported side effects of Mounjaro (tirzepatide) in the UK, affecting more than 1 in 10 people taking the medication. This NHS-aligned guide explains why these effects occur, how long you can expect them to last, and practical steps to manage them. If you're considering Mounjaro through NHS specialist services or private prescription, understanding this side effect will help you prepare and know when to seek support from your GP.
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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 Mounjaro Causes Nausea and How to Manage It
Why sickness happens: Mounjaro works as a dual GIP and GLP-1 receptor agonist, activating hormone pathways that signal fullness to your brain and slow how quickly food leaves your stomach. This slowing effect, called delayed gastric emptying, is particularly common when starting the medication or increasing your dose. Nausea typically appears within the first few days and often improves as your body adjusts over 2–4 weeks.
Managing nausea at home: Eating smaller, more frequent meals rather than large portions can reduce stomach discomfort. Avoid fatty, greasy, or strongly flavoured foods — stick to bland options like toast, rice, and soup. Stay hydrated with water and avoid sugary drinks. Some people find ginger tea helpful, and avoiding rapid position changes can minimise dizziness alongside nausea. If nausea persists beyond 4 weeks, your prescriber may discuss dose adjustments or anti-nausea medication.
When to contact your GP: Seek medical advice if you experience severe, persistent vomiting that prevents you eating or drinking, signs of dehydration, or sickness lasting more than a week without improvement. Your GP can assess whether the dose needs adjusting or if alternative medications might suit you better.
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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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Mounjaro Dose and Sickness: NHS Prescribing Context
In the UK, Mounjaro is prescribed through NHS specialist tier 3 weight management services following referral from your GP, or privately following an online clinical assessment. The standard dose escalation — starting at 2.5 mg and increasing every 4 weeks — is designed to allow your body time to adapt. Nausea is often worse during dose increases; your prescriber will monitor your tolerance and may slow escalation if sickness is severe. Most people find nausea reduces significantly after the first 2–4 weeks, though some experience it intermittently with each dose increase. Using our free GLP-1 weight loss calculator can help you understand realistic timelines for both weight loss and side effect adaptation. Always discuss any concerning symptoms with your GP or prescriber — they can provide personalised advice based on your NHS or private prescription pathway.
- 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 taking Mounjaro?
Nausea typically starts within the first few days and often improves significantly within 2–4 weeks as your body adjusts. It may recur mildly when your dose increases, but usually settles again within a similar timeframe. If nausea persists beyond 4 weeks, contact your GP.
What foods should I eat if Mounjaro is making me sick?
Eat small, frequent meals of bland foods: toast, plain rice, porridge, soup, and boiled vegetables. Avoid fatty, greasy, spicy, or strongly scented foods. Stay hydrated with water and electrolyte drinks. Ginger tea may help some people.
Can my GP change my Mounjaro dose if nausea is severe?
Yes. If nausea is severe, your prescriber may pause dose escalation, reduce your current dose, or discuss alternative options. NHS specialist services and private prescribers can adjust your treatment plan based on how you're tolerating it.
Is nausea with Mounjaro a sign something is wrong?
Mild to moderate nausea is an expected side effect, especially when starting or increasing dose. However, severe vomiting, inability to keep food or fluids down, or signs of dehydration require urgent GP contact to rule out other problems.
Does the nausea mean Mounjaro is working?
Nausea is a side effect related to how the medication affects stomach emptying — it's not a sign of weight loss. Many people experience nausea while still losing weight. Some people have minimal nausea despite significant weight loss.
Ready to take control of your weight loss journey?
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