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 and Mounjaro: How It Compares to Wegovy
Nausea is one of the most common side effects reported with both Mounjaro (tirzepatide) and Wegovy (semaglutide) in clinical trials. Understanding how nausea presents with each medication, and why, can help you make an informed decision alongside your prescriber. This guide compares nausea rates, mechanisms, and management strategies based on UK clinical trial data. Both medications require a prescription and clinical assessment before use.
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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: SURMOUNT vs STEP Data
Mounjaro (tirzepatide) reported nausea in approximately 25–30% of participants in the SURMOUNT-1 trial, with most cases mild to moderate and improving over time. Wegovy (semaglutide) reported nausea in around 25% of participants in the STEP-1 trial, similarly mild to moderate in most cases.
- Mounjaro: Dual GIP and GLP-1 agonist — may cause nausea through dual hormone pathway activation and slowed gastric emptying
- Wegovy: GLP-1 agonist only — single mechanism affecting appetite and stomach emptying
The difference in mechanism (dual vs single) theoretically could affect nausea frequency, but clinical trial data shows comparable rates. Individual experience varies significantly — some people experience no nausea, others more pronounced symptoms. Nausea typically decreases as the body adjusts over weeks to months. Dose titration (gradually increasing from a starting dose) is designed to minimise nausea risk.
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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 Individual Suitability
If you experience nausea with either medication, strategies include eating smaller, regular meals, avoiding fatty foods, staying hydrated, and allowing time for adaptation. Your prescriber may slow your dose escalation or adjust timing. However, persistent severe nausea requires GP discussion — it may not be the right medication for you.
Both Mounjaro and Wegovy require a UK prescription and clinical assessment. Your prescriber will review your medical history, current medications, and nausea risk factors to determine which (if any) is most suitable. No medication is universally better — suitability is individual. If you're concerned about nausea, discuss this with your GP or the prescriber conducting your assessment before starting 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 nausea worse with Mounjaro than Wegovy?
Clinical trials show comparable nausea rates (approximately 25–30% for both). The difference is that Mounjaro uses a dual GIP+GLP-1 mechanism while Wegovy uses GLP-1 only, but this hasn't translated to significantly higher nausea. Individual tolerance varies — some people experience more nausea with one, others with neither.
How long does nausea last with Mounjaro?
In clinical trials, most nausea was mild to moderate and improved within the first few weeks as the body adjusted. By week 8–12, many participants reported decreased nausea. Persistent severe nausea beyond this period warrants GP review.
What can I do to reduce nausea while taking a GLP-1 injection?
Eat smaller, frequent meals; avoid fatty or rich foods; stay well hydrated; and allow time for your body to adjust. Your prescriber may slow your dose escalation schedule. If nausea is severe or persistent, contact your GP immediately.
Does the KwikPen device itself cause nausea?
No. The Mounjaro KwikPen is simply a delivery method for the medication. Nausea comes from the tirzepatide itself, not the injection device. Injection site reactions (redness, bruising) are separate from nausea.
Should I choose Wegovy over Mounjaro to avoid nausea?
Not necessarily — trial data shows similar nausea rates. Your prescriber will assess your individual health profile, eligibility, and suitability. Individual tolerance is unpredictable, so nausea alone isn't a deciding factor. Both require clinical assessment before prescription. ```
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