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 Feel Sick?
Yes, nausea and sickness are among the most commonly reported side effects of Mounjaro in the UK. Clinical trials and real-world NHS use show that feeling sick affects many people taking this tirzepatide injection, particularly during the initial weeks and when doses increase. Understanding what to expect, how long it typically lasts, and when to seek help from your GP is important for anyone considering or starting this prescription medication for weight management.
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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.
Nausea and Sickness on Mounjaro — What the Evidence Shows
Mounjaro (tirzepatide) is a once-weekly GLP-1 and GIP receptor agonist injection licensed in the UK for weight management. Nausea is classified as a very common side effect, meaning it affects more than 1 in 10 people taking the medication. Clinical trials and NHS prescribing data consistently report nausea as the most frequently experienced adverse effect, particularly in the first 4–8 weeks after starting or increasing your Mounjaro KwikPen dose.
- Frequency: Over 25% of trial participants reported nausea at some point
- Severity: Ranges from mild queasiness to significant vomiting requiring dose adjustment or temporary cessation
- Timing: Usually most pronounced in the first few days after injection, improving within 3–5 days for many people
- Dose-related: Nausea often worsens when your dose increases (e.g. moving from 5 mg to 7.5 mg), then typically settles after 1–2 weeks at the new dose
Your GP can discuss what nausea management strategies may help, and whether pausing dose escalation is appropriate for you individually.
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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 NHS Guidance
If you experience nausea on Mounjaro, several practical steps may help: eat smaller, more frequent meals; avoid fatty or greasy foods; stay well hydrated; take your Mounjaro injection at a time when you can rest if needed; and consider ginger tea or other anti-nausea remedies discussed with your GP or pharmacist. Vomiting alongside nausea may indicate you need medical advice—contact your GP practice or NHS 111 if you cannot keep fluids or food down for more than a few hours. Your prescriber may adjust your dose schedule or recommend temporary pause. Using our free GLP-1 weight loss calculator can help you understand what dose level to expect, alongside realistic timelines for side effects settling.
- 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 from Mounjaro typically last?
For most people, nausea peaks in the first 3–5 days after injection and gradually improves over 1–2 weeks. If you're increasing your dose, nausea may return for a few days, then settle again. If nausea persists beyond 2 weeks at the same dose, contact your GP for advice—this is not typical and may need investigation.
Should I stop Mounjaro if I feel sick?
No—do not stop without GP guidance. Mild nausea is expected and usually temporary. However, if you are vomiting repeatedly, unable to eat or drink, or experiencing severe nausea, contact your NHS GP or 111. Your prescriber may pause dose escalation, slow your titration schedule, or adjust your Mounjaro dose. Never adjust your KwikPen dose yourself.
Can I take anti-sickness medication with Mounjaro?
Some anti-sickness medications (anti-emetics) can be used alongside Mounjaro, but discuss this with your GP or pharmacist first. Certain medications may interact or affect how well Mounjaro works. Your prescriber will advise what is safe for you based on your individual health profile and any other medications you're taking.
Is nausea worse on higher Mounjaro doses?
Yes, dose escalation often triggers or worsens nausea temporarily. This is why Mounjaro titration happens gradually—2.5 mg for 4 weeks, then 5 mg, then 7.5 mg, and so on. This slow titration schedule helps your body adjust. If nausea is severe during escalation, your GP may recommend staying at your current dose longer before increasing.
When should I contact my NHS GP about Mounjaro sickness?
Contact your GP if: you are vomiting repeatedly or unable to keep food/fluids down; nausea persists beyond 2 weeks at the same dose; you develop severe abdominal pain alongside nausea (possible pancreatitis); or you feel unable to continue the medication. Your GP can provide individualised support and decide whether to adjust your treatment plan.
Ready to take control of your weight loss journey?
Start with a free BMI check, explore your GLP-1 options, or begin tracking your progress today. No sign-up. No cost. Just results.