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 vs Wegovy — Nausea and Side Effects Compared
Nausea is one of the most common side effects reported with both Mounjaro (tirzepatide) and Wegovy (semaglutide) weight loss injections available in the UK. Both medications work as GLP-1 receptor agonists, though Mounjaro also activates a second pathway (GIP), which may influence how frequently nausea occurs. If you're considering prescription weight loss treatment, understanding how these medications compare on nausea can help you and your prescriber make an informed decision. Individual experiences vary significantly, and the choice between them depends on your personal health profile and clinical suitability.
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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.
Clinical Trial Data — Nausea Rates Compared
Clinical trials provide key insight into nausea frequency with each medication. In the SURMOUNT-1 trial for Mounjaro, nausea was reported by approximately 25–33% of participants depending on dose, with most cases mild to moderate and typically decreasing over time as the body adjusted. The STEP-1 trial for Wegovy reported nausea in approximately 25% of participants at the highest dose (2.4 mg), also typically subsiding within the first few weeks.
- Mounjaro (tirzepatide): Dual GIP + GLP-1 agonist. Nausea often peaks at dose escalations then improves. Average onset: first 2–3 weeks.
- Wegovy (semaglutide): GLP-1 agonist only. Nausea profile similar but potentially slightly less common in early trials, though results are comparable.
- Important context: Trial data shows most participants who experienced nausea rated it mild, and many adjusted without stopping medication.
Both medications slow gastric emptying (how quickly food leaves the stomach), which contributes to nausea — though this effect often reduces over time. Your prescriber can help you manage nausea through dose timing, dietary adjustments, and anti-nausea medication if needed.
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If your BMI suggests you're overweight or obese, explore our GLP-1 calculators to project potential weight loss on Mounjaro or Wegovy.
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Managing Nausea and Individual Suitability
Nausea management with either medication typically involves starting at a low dose and increasing gradually (dose titration), which minimises early side effects. Eating smaller, less fatty meals and staying hydrated can reduce nausea severity. If nausea persists beyond the first few weeks, your GP or prescriber may recommend anti-nausea medication or slower dose escalation.
Neither medication is inherently "better" for nausea — individual responses vary significantly. Some people experience minimal nausea, whilst others find it troublesome. Your prescriber will assess your medical history, other medications, and individual risk factors to determine which is more suitable for you. Both Mounjaro and Wegovy are prescription-only medicines requiring a clinical assessment before dispensing. Use our GLP-1 weight loss calculator to explore potential outcomes with either medication, and discuss nausea management strategies with your prescriber during your consultation.
- 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.
Does Mounjaro cause more nausea than Wegovy?
Clinical trials show nausea rates are comparable between Mounjaro and Wegovy (around 25–33%), though individual experiences vary. Both medications slow stomach emptying, which causes nausea. The difference lies in individual tolerance, not inherent superiority of one over the other. Your prescriber will assess which suits you better based on your health profile.
How long does nausea last with Mounjaro?
Nausea typically peaks during the first 2–3 weeks or after dose increases, then improves as your body adjusts. Most people report mild nausea that subsides within 4–6 weeks. If nausea persists beyond this, inform your GP or prescriber — anti-nausea medication or slower dose titration can help.
Can I manage nausea without stopping the injection?
Yes. Eating smaller, less fatty meals, staying hydrated, and taking anti-nausea medication (prescribed by your GP) are effective strategies. Dose titration (starting low and increasing gradually) also minimises early nausea. Most people manage nausea successfully and continue treatment.
Which GLP-1 injection is best for me — Mounjaro or Wegovy?
Neither is universally "best" — suitability depends on your medical history, other medications, and health conditions. Your prescriber will assess both options during a clinical consultation and recommend the most appropriate one. Both are prescription-only and require clinical assessment in the UK.
What other side effects do Mounjaro and Wegovy share?
Both commonly cause constipation, diarrhoea, stomach pain, and indigestion alongside nausea. Serious side effects (pancreatitis, gallbladder problems) are rare but require urgent medical attention. Always discuss full side effect profiles and your risk factors with your prescriber before starting treatment.
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