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 Feel Sick?
Yes, Mounjaro can cause nausea and other gastrointestinal side effects in many people, particularly when starting the injection or increasing doses. Nausea is listed as a very common side effect — affecting more than 1 in 10 people in clinical trials. However, it often improves over time as your body adjusts to the medication. Understanding what to expect and how to manage these effects can help you decide whether this prescription-only tirzepatide injection is right for you, and what support your GP can offer during treatment.
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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 With Mounjaro?
Nausea is the most frequently reported side effect of Mounjaro (tirzepatide), a dual GIP and GLP-1 receptor agonist used for weight management in UK adults. Clinical data shows nausea affects more than 1 in 10 people using this prescription injection.
Other very common gastrointestinal side effects include diarrhoea, vomiting, constipation, and stomach pain. These effects typically occur when:
- Starting Mounjaro for the first time
- Increasing to a higher dose (the KwikPen doses escalate from 2.5 mg up to 15 mg)
- During the first few weeks of treatment
For most people, nausea tends to decrease significantly after the first 4–8 weeks as your body adjusts to the medication. The good news is that nausea usually does not mean the injection is unsafe — it is a recognised adjustment effect. If you are using our GLP-1 weight loss calculator, you can explore potential outcomes at different doses before speaking to your prescriber about which dose might suit you.
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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 When to Seek Help
If you experience nausea while taking Mounjaro, several practical steps may help: eat smaller, more frequent meals; avoid fatty or greasy foods; stay hydrated; take ginger supplements or peppermint tea; and take your injection at a consistent time each week.
Contact your GP or prescriber if:
- Nausea is severe or persistent after 8 weeks
- You cannot keep food or fluids down
- You develop severe, persistent stomach pain spreading to your back (possible pancreatitis)
- You experience signs of dehydration (dark urine, dizziness, extreme thirst)
- Nausea prevents you from taking other essential medications
Your healthcare team can offer additional support, adjust your dose, or discuss whether Mounjaro remains the right option for you. You can also track your symptoms and weight progress using our free progress tracker to share with your 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 usually last?
For most people, nausea peaks in the first 1–2 weeks after starting or increasing a dose, then gradually improves over 4–8 weeks as your body adjusts. Some people experience minimal nausea, while others take longer to adapt. If nausea persists beyond 8 weeks or is severe, speak to your GP.
Is nausea a sign that Mounjaro is not working?
No. Nausea is a common adjustment side effect and does not indicate whether the weight loss injection will be effective for you. In fact, many people who experience nausea go on to lose weight successfully once the nausea settles. Results vary between individuals.
Can I stop Mounjaro if I feel sick?
Do not stop suddenly without medical advice. Speak to your prescriber first — they may adjust your dose, give you time to adjust, or recommend strategies to manage nausea. Stopping suddenly is not advised as your body needs to readjust, and your prescriber needs to assess whether this medication is still suitable for you.
What's the difference between Mounjaro and Wegovy nausea?
Both Mounjaro (tirzepatide) and Wegovy (semaglutide) are prescription GLP-1 based injections that commonly cause nausea. Mounjaro is a dual GIP and GLP-1 agonist, while Wegovy is GLP-1 only. Clinical trial data suggests nausea rates are similar, though individual experience varies. Your prescriber can advise which is more suitable for you.
Should I eat differently to reduce Mounjaro nausea?
Yes. Eat smaller meals more frequently, avoid high-fat foods, stay well hydrated, and eat slowly. Some people find eating bland foods like rice, toast, or bananas helpful. Avoid strong smells and eat foods at cooler temperatures. If nausea is very severe, speak to your GP — they may suggest antiemetic medication or dietary advice tailored to 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.