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
Free tracker included with every download this week
Why Does Mounjaro Cause Sickness?
Nausea and sickness are among the most common side effects when starting Mounjaro (tirzepatide), a prescription-only weight management injection licensed in the UK. Many people experience some level of nausea, particularly during the first few weeks or when increasing doses. This happens because Mounjaro works by activating GLP-1 and GIP hormone pathways that slow how quickly food moves through your stomach and signal fullness to your brain. While uncomfortable, nausea typically improves over time as your body adjusts. Understanding what to expect and how to manage it can help you stay on track with treatment. Always speak to your prescriber if sickness becomes severe or unbearable.
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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.
How Common Is Nausea on Mounjaro?
Clinical trial data shows nausea is very common when starting Mounjaro. In the SURMOUNT-1 trial, nausea was reported by over 25% of participants taking Mounjaro, making it one of the most frequent side effects — though it is not inevitable and severity varies widely between individuals.
Nausea is most likely to occur:
- In the first 4 weeks after starting Mounjaro
- When increasing to a new dose (often lasting 3–7 days then improving)
- On an empty stomach or after eating fatty or heavy foods
- If you eat too quickly or in larger portions than before
The good news is that for most people, nausea tends to reduce significantly after 2–4 weeks as the body adjusts to the medication. However, some people experience mild nausea throughout their treatment. This is different from the dose escalation schedule used with Mounjaro UK prescription protocols, where doses increase gradually to minimise adjustment side effects.
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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 Ways to Manage Mounjaro Sickness
Dietary changes can significantly reduce nausea. Eat smaller, more frequent meals rather than three large ones. Avoid fatty, greasy, or spicy foods immediately after your injection, and stay hydrated with water and clear fluids. Ginger tea, mint tea, and eating slowly can also help. Some people find that taking their Mounjaro injection in the evening, then eating lightly the next day, reduces sickness.
If nausea persists or worsens, contact your prescriber — they may recommend an anti-nausea medication, suggest adjusting when you eat relative to your injection, or pause dose escalation briefly. Do not stop Mounjaro without medical guidance. Track your symptoms using our free progress tracker to identify patterns and share them with your GP or prescriber.
- 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 Mounjaro nausea last?
Most people experience nausea for 3–7 days after starting or increasing their dose, then it improves significantly. However, some people have mild ongoing nausea throughout treatment. If nausea persists beyond 2 weeks or worsens, contact your prescriber for guidance. Everyone responds differently — patience is key.
Can I take anti-sickness medication with Mounjaro?
Yes, your prescriber or GP can recommend anti-nausea medication if needed. Common options include ginger supplements, ondansetron, or cyclizine. Always inform your prescriber of any other medications you take, as Mounjaro may affect how some oral medications are absorbed.
Should I stop Mounjaro if I feel sick?
Do not stop Mounjaro without speaking to your prescriber first. Nausea often improves naturally over time. Your prescriber may recommend dietary changes, anti-nausea medication, delaying your next dose increase, or other adjustments before considering stopping treatment.
Is Mounjaro sickness the same as Wegovy nausea?
Both Mounjaro (tirzepatide) and Wegovy (semaglutide) cause nausea commonly, as they both work on appetite regulation pathways. However, Mounjaro is a dual GIP and GLP-1 agonist while Wegovy is GLP-1 only, so individual experiences vary. Your prescriber can discuss which medication might suit you better.
What should I eat if Mounjaro makes me feel sick?
Eat bland, easily digestible foods: boiled chicken, rice, toast, crackers, soup, and soft fruits. Avoid fried foods, high-fat dairy, caffeine on an empty stomach, and spicy dishes. Eat slowly in small portions. Staying hydrated with water, herbal tea, and clear broths also helps. Keep a food diary to identify triggers — use our GLP-1 weight loss calculator to track alongside dietary patterns.
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.