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
Why Does Mounjaro Make You Feel Sick?
Nausea and sickness are very common side effects of Mounjaro (tirzepatide) in the UK. Understanding why this happens helps you manage it effectively. The sickness occurs because Mounjaro works by slowing how quickly food leaves your stomach and activating appetite-control pathways in your brain. These effects are normal, usually temporary, and often improve as your body adjusts during the dose titration process. This guide explains the mechanism behind Mounjaro-related nausea and what you can do about it.
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.
How Mounjaro Causes Nausea and Sickness
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist — it activates two natural hormone pathways that regulate appetite and digestion. This dual mechanism is what sets it apart from other weight loss injections like Wegovy. When you inject Mounjaro once weekly, it signals your brain that you are fuller sooner and reduces food cravings. Additionally, it slows gastric emptying — the rate at which food moves from your stomach into your small intestine. This slower digestion can trigger nausea, especially if you eat larger portions or fatty foods.
Sickness is listed as a very common side effect in UK prescribing information, affecting more than 1 in 10 people. The nausea is typically worst in the first few weeks after starting Mounjaro or when increasing your dose (during dose titration). Your stomach lining contains GLP-1 receptors, and when Mounjaro activates them, this can directly cause queasiness. Most people find that nausea peaks around days 2–4 after injection and gradually improves as your body adjusts.
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.
Managing Mounjaro Sickness and When to Contact Your GP
If you experience sickness on Mounjaro in the UK, speak to your GP or the prescriber managing your treatment. Practical steps include eating smaller, more frequent meals; avoiding fatty or greasy foods; staying hydrated; and resting after meals. Some people find ginger tea or anti-nausea remedies helpful, though always discuss these with your GP first. If nausea is severe, persistent, or prevents you from eating and drinking, contact your GP — they may recommend pausing your injection or adjusting your dose schedule.
Seek urgent medical attention if you experience severe stomach pain spreading to your back (possible pancreatitis), persistent vomiting, or signs of dehydration. These are different from mild nausea and require immediate evaluation. Remember, sickness typically improves within 1–2 weeks as your body adapts, especially during dose titration when you are building up gradually.
- 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 nausea go away?
Yes, for most people. Nausea is very common in the first 1–2 weeks after starting Mounjaro or increasing your dose, but typically improves as your body adjusts. This process is called tolerance. By week 3–4, many people notice sickness improving significantly. If nausea persists beyond 4 weeks, contact your GP.
How is Mounjaro nausea different from Wegovy nausea?
Both Mounjaro and Wegovy cause nausea because they both slow stomach emptying and reduce appetite. Mounjaro's dual GIP and GLP-1 mechanism may cause slightly different nausea patterns than Wegovy's single GLP-1 action, but individual experiences vary widely. Your prescriber can discuss which might suit you better.
Can I take anti-nausea medication with Mounjaro?
Always ask your GP or prescriber before taking anti-nausea medicines. Some medications may interact with Mounjaro or affect how well it works. Your prescriber may recommend specific safe options. Never self-medicate without checking first.
Should I stop taking Mounjaro if I feel sick?
Do not stop your Mounjaro injection without talking to your prescriber. Sickness is usually temporary and manageable. However, if nausea is severe, preventing you from eating or drinking, or accompanied by severe stomach pain, contact your GP immediately for guidance.
Is feeling sick a sign Mounjaro is working?
Nausea does not mean Mounjaro is working more effectively. It is simply a side effect of how the medication affects your stomach and appetite signals. Some people experience minimal nausea but still lose weight successfully. Side effects and weight loss outcomes are separate.
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.