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 on Mounjaro vs Wegovy — What the Evidence Shows
Nausea is one of the most common side effects of both Mounjaro (tirzepatide) and Wegovy (semaglutide) — affecting more than 1 in 10 people in clinical trials. But are you more likely to experience sickness on one rather than the other? This guide compares the evidence from the SURMOUNT and STEP trials, explains why these injections cause nausea, and helps you understand what to expect if you're prescribed either medication. Both Mounjaro and Wegovy are prescription-only weight loss injections available in the UK through NHS specialist services or following a private clinical assessment.
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Enter your height and weight below. Supports both imperial (stone & lbs) and metric (kg). Results include NHS category, healthy weight range, and ethnicity adjustments.
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.
Mounjaro vs Wegovy — Nausea in Clinical Trials
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist — it activates two hormone pathways rather than one. In the SURMOUNT-1 clinical trial, nausea was reported by approximately 25–26% of participants across all doses, with severity often decreasing after the first few weeks. Nausea was the most common reason for study withdrawal in the first weeks.
Wegovy (semaglutide) is a single GLP-1 receptor agonist. In the STEP-1 trial, nausea affected approximately 25% of participants on the 2.4 mg dose — similar frequency to Mounjaro, but potentially presenting differently due to semaglutide's single mechanism.
- Both medications slow gastric emptying (how quickly food leaves the stomach), which directly triggers nausea
- Nausea is typically worse during dose escalation phases
- Most people experience nausea reduction within 4–8 weeks as the body adapts
- Individual tolerance varies significantly — some people experience minimal nausea, others find it limiting
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Three simple steps to understand your weight and take action.
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 Between Them
Neither Mounjaro nor Wegovy is inherently "less nausea-inducing" — the difference is individual. Your prescriber will assess which suits you based on your personal tolerance, other health conditions, and dose escalation preference. Mounjaro requires slower titration (starting at 2.5 mg, taking 4+ weeks between increases), which some people find easier for nausea management. Wegovy starts lower (0.25 mg) but escalates faster.
Managing sickness while on either medication:
- Eat small, frequent meals rather than large ones
- Avoid fatty, greasy, or strongly flavoured foods
- Stay hydrated — sip water throughout the day
- Consider ginger tea or peppermint (some evidence supports these)
- Tell your prescriber if nausea is severe — dose adjustment may help
- Track your symptoms using our free progress tracker to identify patterns
- 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 on Mounjaro or Wegovy?
Clinical trial data shows similar nausea rates (~25% on both), but individual experience varies greatly. The dual mechanism of Mounjaro may feel different to some people compared to Wegovy's single GLP-1 action, but neither is objectively "worse". Your GP or prescriber can discuss which is more likely to suit you personally.
How long does nausea last on these medications?
Most people experience nausea reduction within 4–8 weeks as the body adapts. Nausea is often worst during dose escalation. If sickness persists beyond 12 weeks or is severe, contact your prescriber — dose adjustment or switching medications may be appropriate.
Can I take anti-sickness medication with Mounjaro or Wegovy?
Some anti-nausea medications are safe to use alongside these injections, but you must discuss this with your GP or prescriber first. They'll advise based on your specific situation and any other medications you take. Do not self-prescribe anti-sickness medication.
What's the difference between Mounjaro and Wegovy that causes nausea?
Mounjaro activates both GIP and GLP-1 pathways (dual action), while Wegovy activates GLP-1 only. Both slow stomach emptying, which causes nausea. Mounjaro's dual mechanism may affect appetite and fullness differently, but nausea rates in trials were similar. Individual response varies regardless of mechanism.
If I'm sick on Mounjaro, will I be sick on Wegovy too?
Not necessarily. While both cause nausea in similar proportions, some people tolerate one better than the other due to individual biology. If sickness on one becomes unmanageable, your prescriber can discuss switching. Use our free GLP-1 weight loss calculator to explore both options and discuss tolerability with your GP.
Ready to take control of your weight loss journey?
Start with a free BMI check, explore your GLP-1 options, or begin tracking your progress today. No sign-up. No cost. Just results.