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
Understanding Mounjaro-Related Vomiting and Nausea
Vomiting and nausea are among the most common side effects reported by people taking Mounjaro (tirzepatide) in the UK. These occur because Mounjaro activates GLP-1 and GIP hormone pathways that naturally signal fullness and slow stomach emptying. While throwing up can be distressing, it typically improves as your body adjusts to the medication. This guide explains why vomiting happens, what NHS guidance recommends, and when to seek help from your GP.
10,000+ calculations today · NHS-aligned thresholds · 100% free
Calculate Your BMI Instantly
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 Vomiting
Mounjaro works by mimicking natural gut hormones (GIP and GLP-1) that regulate appetite and blood sugar. As a dual GIP and GLP-1 receptor agonist, it slows how quickly food leaves your stomach and signals to your brain that you're full — effects that can trigger nausea, especially when you first start the medication or increase your dose.
Vomiting is classified as "very common" in clinical trials, occurring in more than 1 in 10 people. Most episodes happen during the first few weeks or after a dose increase. The severity typically peaks within days and then gradually improves as your body adjusts. NHS guidance emphasises that this is not a sign the medication isn't working — it's simply your system adapting to these new hormonal signals. Eating smaller, lighter meals and staying hydrated can help manage symptoms while your body acclimatises.
Clinically BackedWeight Loss
No appointments. No waiting rooms. Just care — from a UK-regulated online pharmacy.
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.
NHS Guidance and When to Contact Your GP
If you experience persistent vomiting, contact your GP immediately, especially if you cannot keep fluids down for more than a few hours — this risks dehydration. Your GP may suggest temporarily pausing dose increases, slowing the titration schedule, or checking that you're not taking Mounjaro on an empty stomach. For manageable nausea, small frequent meals, avoiding fatty or spicy foods, and ginger supplements may help. If vomiting is severe or doesn't improve after several weeks, your prescriber may recommend switching to an alternative medication or adjusting your treatment plan. Never stop Mounjaro abruptly without GP 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.
Is vomiting on Mounjaro normal?
Yes. Vomiting is very common in the first few weeks as your body adjusts to the medication's effects on appetite regulation. Clinical trials show it affects more than 1 in 10 people. Most improve within 2–4 weeks as your system adapts. Contact your GP if it persists beyond this or is severe.
Does vomiting mean Mounjaro isn't working?
No. Nausea and vomiting are side effects of how Mounjaro works — not indicators of efficacy. The medication's weight loss benefits are separate from these adjustment symptoms. Most people continue the medication and find side effects improve over time.
What should I eat if I'm feeling nauseous on Mounjaro?
Eat small, frequent meals with bland, low-fat foods like toast, rice, soup, or crackers. Avoid greasy, spicy, or heavy meals. Stay hydrated with water, herbal tea, or electrolyte drinks. Some people find ginger helpful. Never skip meals entirely, as this can worsen nausea.
When should I contact my GP about Mounjaro vomiting?
Contact your GP if you cannot keep any fluids down for several hours, have signs of dehydration (dizziness, dark urine), vomit persistently beyond 4 weeks, or suspect vomiting may mask a more serious condition like pancreatitis. Severe stomach pain alongside vomiting requires urgent medical attention.
Can my GP adjust my Mounjaro dose if vomiting is severe?
Yes. Your GP or specialist can pause your dose increase, extend the titration timeline, or switch you to a different medication. Some people manage side effects better on a lower maintenance dose. Always discuss symptoms with your prescriber — they can personalise your treatment plan based on your tolerance.
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.