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
Free tracker included with every download this week
Feel Sick On Mounjaro — What You Need to Know
Nausea is one of the most common side effects when starting Mounjaro (tirzepatide), especially during the initial dose titration phase. If you're feeling sick on Mounjaro, you're not alone — many people experience this as their body adjusts to the medication. This guide explains why nausea happens, how long it typically lasts, when to contact your GP, and what access and cost options are available in the UK for those considering or currently taking this prescription weight management injection.
10,000+ calculations today · NHS-aligned thresholds · 100% free
Calculate Your BMI Instantly
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.
Why Nausea Happens on Mounjaro and Managing It
Nausea on Mounjaro is very common — affecting more than 1 in 10 people in clinical trials. It typically occurs because tirzepatide slows how quickly food leaves your stomach and reduces appetite signals to the brain. Nausea is often worse when starting the medication or during dose increases, and usually improves within a few days to a week as your body adapts.
How to manage nausea:
- Eat smaller, more frequent meals rather than large ones
- Avoid fatty, greasy, or spicy foods
- Stay hydrated with small sips of water throughout the day
- Take your injection on a day when you can rest if possible
- Avoid strong smells or foods that trigger nausea
- Ginger tea or peppermint may help some people
If nausea is severe, persistent (lasting more than a week), or accompanied by vomiting, contact your GP or prescriber immediately. Your prescriber may recommend taking the medication with food, adjusting the dose timing, or in rare cases, pausing treatment while you adjust. Never stop taking Mounjaro without medical advice.
Clinically BackedWeight Loss
No appointments. No waiting rooms. Just care — from a UK-regulated online pharmacy.
How It Works
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.
Free Weight Loss Tools & Guides
Everything you need to understand your weight, explore medication options, and track your progress — completely free.
Accessing Mounjaro in the UK — NHS vs Private Routes and Costs
In the UK, Mounjaro (tirzepatide) is available through two routes: NHS specialist services and private online prescribing. NHS access is through tier 3 or 4 weight management services, typically requiring a GP referral. Availability varies significantly by region and waiting lists can be lengthy — sometimes many months. Private prescriptions are available through GPhC-registered online pharmacies following a clinical assessment with a UK-licensed prescriber, usually within 24–48 hours. Private costs range from approximately £129–£320 per month depending on dose, with 2.5 mg starting doses at the lower end and 15 mg (maximum) at the higher end. Whichever route you use, Mounjaro is always prescription-only and requires ongoing medical oversight, particularly if you experience persistent side effects like nausea.
- 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.
How long does nausea last when starting Mounjaro?
Nausea typically peaks in the first few days after an injection and often improves within 3–7 days as your body adjusts. Some people experience mild nausea throughout their treatment, whilst others have none. If nausea persists beyond a week or worsens, speak to your prescriber — dose adjustment or timing changes may help.
Can I get Mounjaro on the NHS in the UK?
Yes, Mounjaro is approved by NICE for use within NHS specialist weight management services. However, access is through tier 3 services requiring GP referral, and availability varies significantly by region. Waiting times can be several months. Your GP can advise whether you meet eligibility criteria and how to access your local service.
What's the typical cost of Mounjaro on private prescription in the UK?
Private Mounjaro costs range from approximately £129–£320 per month depending on the dose. Starting doses (2.5 mg) are typically cheaper than maximum doses (15 mg). Prices vary between GPhC-registered pharmacies, so it's worth comparing. Some pharmacies offer package deals for multiple months.
Should I stop taking Mounjaro if I feel sick?
Never stop Mounjaro without medical advice, even if nausea is uncomfortable. Contact your prescriber or GP instead — they can suggest management strategies, adjust your dose timing, or recommend pausing temporarily if necessary. Sudden cessation can cause other issues, so always get professional guidance first.
Is Mounjaro nausea different from Wegovy nausea?
Both Mounjaro and Wegovy can cause nausea, but Mounjaro's dual GIP/GLP-1 mechanism may affect some people differently than Wegovy's single GLP-1 mechanism. Individual responses vary widely. If you're experiencing intolerable nausea on either medication, discuss alternatives with your prescriber — they can advise whether switching might help.
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.