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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Mounjaro Throwing Up vs Wegovy — What's the Difference?
Nausea and vomiting are common side effects of both Mounjaro (tirzepatide) and Wegovy (semaglutide), but the frequency and severity can differ between the two medications. Both are prescription-only GLP-1 based weight loss injections licensed in the UK, but they work through different mechanisms. Understanding how each medication compares can help you and your prescriber decide which might be more suitable for you following a clinical assessment.
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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 Mounjaro and Wegovy Compare for Nausea and Vomiting
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, whereas Wegovy (semaglutide) activates GLP-1 only. This mechanism difference may influence side effect profiles. In the SURMOUNT-1 clinical trial, nausea was reported by over 25% of participants on Mounjaro 15mg, with vomiting in around 12% of the highest-dose group. In the STEP-1 trial for Wegovy, nausea affected approximately 25% of participants on the maximum 2.4mg dose, with vomiting in around 11%. Both medications show that gastrointestinal side effects are most common during dose escalation and typically reduce over time as your body adjusts. The frequency of vomiting generally decreases after the initial titration phase. Individual tolerance varies significantly — some people experience minimal symptoms whilst others find nausea more pronounced. Your prescriber will discuss strategies to manage these effects, including taking the injection at a consistent time, adjusting diet, and staying hydrated.
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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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Which Medication Might Be Better for You?
There is no clear evidence that one medication causes significantly less nausea than the other — trial data shows comparable rates. Your individual experience depends on factors including your metabolism, how quickly you escalate doses, your diet, and your baseline sensitivity to GLP-1 effects. Some people find that side effects are manageable with practical strategies like eating smaller meals, avoiding fatty or greasy foods, and staying well hydrated. If nausea becomes severe or persistent beyond the titration phase, your prescriber may adjust your dose, slow your escalation, or consider switching medications. Use our free GLP-1 weight loss calculator to explore potential outcomes with either medication, and discuss your concerns with your prescriber — they can personalise your treatment plan based on your health history and preferences. Both Mounjaro and Wegovy require a prescription following a clinical assessment, and your prescriber will monitor your response throughout treatment.
- 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 more common with Mounjaro or Wegovy?
Clinical trial data shows similar rates of vomiting between the two medications — around 11–12% at maximum doses. Individual experiences vary significantly. Both medications show that vomiting is most common during dose escalation and typically improves as your body adjusts over several weeks.
Can nausea be managed without stopping the medication?
Yes. Practical strategies include eating smaller, more frequent meals; avoiding fatty or greasy foods; staying hydrated; taking the injection at a consistent time; and resting after eating. If nausea is severe, your prescriber may slow your dose escalation or adjust your timing.
How long does throwing up typically last on these medications?
Vomiting is usually most pronounced during the first 4–8 weeks of dose escalation. Most people find symptoms improve significantly after the titration phase as their body adjusts. If vomiting persists beyond 12 weeks, contact your prescriber.
Does the dual mechanism of Mounjaro cause more nausea than Wegovy's single GLP-1 action?
Not necessarily. Trial data shows comparable nausea rates between the two medications despite their different mechanisms. The GIP component of Mounjaro may influence individual responses, but this isn't reflected in significantly higher side effect rates in clinical trials.
How do I decide between Mounjaro and Wegovy if I'm worried about vomiting?
This is a discussion for your prescriber. Factors include your individual health history, any previous medication responses, gastrointestinal conditions, and personal preference. Both medications require a clinical assessment before prescription, and your prescriber can advise which is more suitable for you.
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