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 Nausea vs Wegovy — Which Causes More?
Nausea is a common side effect with both Mounjaro (tirzepatide) and Wegovy (semaglutide), but the frequency and severity may differ between the two medications. Both are prescription-only weight loss injections licensed in the UK, and both work by activating similar but slightly different pathways in the body. Understanding how nausea compares can help you and your prescriber decide which medication might suit you better. This guide compares the clinical trial data, mechanisms, and practical considerations for both treatments.
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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.
Nausea in Clinical Trials — Mounjaro vs Wegovy
Mounjaro (tirzepatide) in SURMOUNT trials: Nausea was reported by up to 25–30% of participants at the highest doses, typically occurring during the dose escalation phase and often improving over time as the body adjusts.
Wegovy (semaglutide) in STEP trials: Nausea affected approximately 25% of participants at the maximum dose, with similar timing — most common during early weeks and dose increases.
The key difference lies in the mechanism: Mounjaro is a dual GIP and GLP-1 receptor agonist, activating two hormone pathways simultaneously, whilst Wegovy activates only the GLP-1 pathway. This dual mechanism in Mounjaro may contribute to faster appetite suppression but does not necessarily mean more nausea — individual responses vary considerably. The nausea in both medications is typically dose-dependent, meaning lower doses (5 mg Mounjaro, 0.5 mg Wegovy) often cause less nausea than maximum doses (15 mg Mounjaro, 2.4 mg Wegovy).
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Managing Nausea and Finding the Right Fit
Both medications can cause nausea, but it often improves within 2–4 weeks as your body adjusts. Your prescriber may recommend starting at the lowest dose and increasing gradually — this is called dose titration — to minimise nausea. Some patients find that staying on a lower, well-tolerated dose provides good weight loss results without escalating to the maximum dose.
Neither medication is inherently "better" for nausea; suitability depends on your individual health profile, any other medications you take, and previous experiences with similar treatments. Calculate your estimated weight loss using our free GLP-1 weight loss calculator, and discuss medication options with your prescriber. Your GP or licensed prescriber will assess which medication aligns best with your health needs and tolerance.
- 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 trial data shows nausea rates are similar — approximately 25–30% at maximum doses for both. However, individual experiences vary significantly. Some people tolerate one medication better than the other due to differences in how their body responds to the dual GIP+GLP-1 mechanism (Mounjaro) versus single GLP-1 mechanism (Wegovy). Your prescriber can help determine which suits you based on your health profile.
When does nausea typically start with Mounjaro or Wegovy?
Nausea usually appears within the first 1–2 weeks of starting or increasing a dose, and often improves by week 3–4 as your body adapts. If nausea persists or worsens, inform your prescriber — they may adjust your dose or recommend strategies to manage it, such as eating smaller meals or taking the injection at a different time of day.
Can I reduce nausea by staying on a lower dose?
Yes. Both Mounjaro and Wegovy show dose-dependent effects — lower doses typically cause less nausea. Many people achieve meaningful weight loss at moderate doses (Mounjaro 5–10 mg, Wegovy 1–1.7 mg) without needing the maximum dose. Discuss your tolerance and weight loss goals with your prescriber to find the best dose for you.
What's the difference between Mounjaro and Wegovy mechanisms?
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist — it activates two appetite-regulating pathways. Wegovy (semaglutide) activates only the GLP-1 pathway. This dual mechanism may help Mounjaro work slightly faster, but both cause similar nausea rates in clinical trials. Individual response varies.
How do I know which medication is right for me?
Only a UK-licensed prescriber can assess this following a clinical evaluation of your health, BMI, medical history, and any other medications you take. Both are prescription-only and require clinical assessment. Ask your GP or prescriber about eligibility, side effect profiles, and which aligns best with your health needs. Use our BMI calculator to understand your starting point before your consultation. ```
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