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
Can Mounjaro Make You Vomit?
Yes, nausea and vomiting are common side effects of Mounjaro (tirzepatide), particularly when you first start the medication or when your dose increases. NHS guidance shows these symptoms affect many people taking this prescription weight management injection, but they typically improve over time as your body adjusts. Understanding what to expect and how to manage these effects can help you decide whether Mounjaro is right for you. Most side effects are temporary and manageable with proper support from your prescriber.
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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 Are Nausea and Vomiting With Mounjaro?
Nausea is one of the most frequently reported side effects of Mounjaro in the SURMOUNT clinical trials that led to NHS approval. Clinical data shows nausea affects more than 1 in 10 people taking tirzepatide, making it a "very common" side effect in medical terms. Vomiting is less common than nausea but still affects a significant proportion of users, particularly in the first four weeks of treatment or when increasing your Mounjaro KwikPen dose.
- Peak nausea often occurs 1–3 days after your weekly injection
- Symptoms typically peak in weeks 1–4 and improve as your body adjusts
- Higher doses (10mg and 15mg) are associated with higher rates of nausea than lower starting doses
- Individual tolerance varies significantly — some people experience minimal symptoms while others struggle more
Your GP or prescriber should discuss this before you start, as dose titration (starting low and gradually increasing) helps many people manage these effects better than jumping straight to higher doses.
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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 Nausea and Vomiting — Practical Strategies
If you experience nausea or vomiting while taking Mounjaro, several practical strategies can help. Eating smaller, more frequent meals rather than three large ones reduces strain on your digestive system. Avoid fatty, greasy, or spicy foods — stick to bland options like toast, rice, chicken, and vegetables. Stay hydrated by sipping water regularly throughout the day, and avoid sugary drinks which can worsen nausea.
- Take your injection on a day when you can rest if needed (Friday or weekend often works well)
- Ginger tea or peppermint can help settle your stomach naturally
- Slow down your eating pace — rushing makes nausea worse
- Tell your GP or prescriber if symptoms persist beyond 2–3 weeks
Anti-sickness medication is available on prescription if nausea becomes severe, so always contact your healthcare provider rather than stopping the medication without guidance.
- 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.
When does nausea from Mounjaro typically start?
Nausea usually begins within 24–48 hours of your Mounjaro KwikPen injection and tends to peak around day 2–3. For most people, it improves by day 5–6 as your body adjusts. This pattern often repeats with each new dose, but generally becomes less severe over the first month of treatment as your system becomes accustomed to the tirzepatide.
Should I stop taking Mounjaro if I'm vomiting?
Do not stop without contacting your prescriber first. Vomiting alone is not usually a reason to discontinue Mounjaro — instead, speak to your GP or the prescriber who issued your prescription. They may suggest dose reduction, switching injection days, anti-sickness medication, or dietary adjustments. Stopping suddenly without guidance is not recommended.
Is nausea from Mounjaro permanent?
No. For most people, nausea improves significantly within 2–4 weeks as your body adapts to the medication. Clinical trial data shows that while nausea is very common initially, tolerability improves over time. Some people experience persistent mild nausea, but severe long-term nausea is relatively uncommon and warrants discussion with your prescriber.
Can I use the NHS or private route for Mounjaro in the UK?
Yes, both routes exist. NHS access is through tier 3 specialist weight management services (you need a GP referral and eligibility based on BMI and health conditions). Private access is through GPhC-registered online pharmacies following a clinical assessment with a UK-licensed prescriber — no NHS referral needed. NHS availability varies significantly by region.
Does Mounjaro cause vomiting more than Wegovy?
Both Mounjaro (tirzepatide) and Wegovy (semaglutide) can cause nausea and vomiting. While direct clinical comparisons show similar rates, some evidence suggests tirzepatide may cause slightly more gastrointestinal side effects in early treatment phases. Individual responses vary considerably, so your personal experience may differ from general trends. Your prescriber can help choose the best option for you.
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.