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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Nausea With Mounjaro vs Wegovy — What the Evidence Shows
Nausea is one of the most common side effects reported with both Mounjaro (tirzepatide) and Wegovy (semaglutide) during the early weeks of treatment. Both medications work as GLP-1 receptor agonists (or in Mounjaro's case, a dual GIP and GLP-1 agonist), and nausea typically occurs when starting or increasing doses. This guide compares nausea rates between the two UK-licensed weight loss injections, explains why it happens, and helps you understand what prescribers consider when choosing between them. Individual responses vary significantly, so personal suitability is always assessed by your healthcare provider.
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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 Comparison
Clinical trials provide the clearest picture of how common nausea is with each medication:
- Mounjaro (SURMOUNT-1 trial): Nausea occurred in approximately 25–30% of participants on the highest dose (15 mg), with most reporting it as mild to moderate and temporary
- Wegovy (STEP-1 trial): Nausea occurred in approximately 25% of participants on the maximum dose (2.4 mg), typically mild to moderate severity
Both medications show similar nausea prevalence in clinical trials. The key difference lies in mechanism and timing: Mounjaro's dual GIP and GLP-1 action may produce slightly different nausea patterns than Wegovy's single GLP-1 mechanism, though individual variation is substantial. Nausea almost always improves or resolves completely within 2–4 weeks as your body adjusts. Your prescriber will monitor your response and can adjust your dose titration schedule if needed.
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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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Managing Nausea and Choosing the Right Medication for You
If you experience nausea with either medication, practical strategies can help: eating smaller, frequent meals; staying hydrated; avoiding fatty or greasy foods; and taking your time with digestion. Some people find ginger or peppermint tea helpful. Most importantly, do not stop taking your injection without speaking to your prescriber—adjusting the dose schedule or temporarily pausing escalation often resolves nausea without stopping treatment altogether.
Choosing between Mounjaro and Wegovy is not based on nausea alone. Your GP or prescriber will consider your overall health, any other medications you take (especially if you use oral contraceptives, which Mounjaro may affect), your BMI, and any weight-related health conditions. Use our free GLP-1 weight loss calculator to explore potential outcomes, and our BMI calculator to understand your current health context before 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.
Is nausea more common with Mounjaro or Wegovy?
Clinical trials show similar nausea rates—approximately 25–30% on highest doses for both. Individual responses vary. Mounjaro's dual mechanism (GIP and GLP-1) may produce different nausea timing than Wegovy's single GLP-1 action, but neither is clearly superior. Your prescriber will monitor your specific response and adjust accordingly.
How long does nausea last when starting Mounjaro?
Nausea typically peaks within the first 1–2 weeks after starting or increasing a dose, then improves over 2–4 weeks as your body adjusts. Most people find it mild to moderate. Eating smaller meals, staying hydrated, and avoiding fatty foods helps. Always inform your prescriber if nausea is severe or persistent.
Can I switch from Mounjaro to Wegovy if nausea is too much?
Possibly—but discuss this with your prescriber first. Often, adjusting the dose titration schedule (slowing the increase) or pausing at a lower dose resolves nausea without switching. A UK prescriber will assess whether switching is appropriate and manage the transition safely, as the two medications have different starting doses and escalation protocols.
Will nausea prevent me from losing weight on Mounjaro?
Not necessarily. Nausea and appetite suppression are separate effects. Many people report significant weight loss despite mild nausea in the early weeks. As nausea resolves, appetite-suppressing benefits continue. Your progress tracker can help you monitor both symptom improvement and weight loss over time.
How do GLP-1 only (Wegovy) and dual GIP/GLP-1 (Mounjaro) mechanisms affect nausea differently?
Mounjaro's additional GIP action may affect gastric motility differently than Wegovy's single GLP-1 effect, potentially causing slightly different nausea patterns. However, clinical trial data shows comparable overall nausea rates. Individual variation is more significant than the mechanism difference—some people tolerate one better than the other, which your prescriber can help assess.
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