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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Can Mounjaro Make You Sick?
Yes, Mounjaro (tirzepatide) can cause nausea and other side effects, particularly when starting treatment or increasing doses. Nausea is one of the most common side effects reported in clinical trials, affecting a significant proportion of people using this prescription-only weight management injection. Understanding what to expect, how long side effects typically last, and whether they're serious enough to stop treatment is essential before starting. This guide explains Mounjaro's side effects in a UK context, and covers both NHS and private access routes so you can make an informed decision about cost and availability.
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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.
Common Side Effects and Managing Nausea
Nausea is the most frequently reported side effect when starting Mounjaro or increasing your dose. Clinical trials showed that nausea affected more than 1 in 10 people taking the injection, particularly in the first few weeks. The good news is that nausea often reduces over time as your body adjusts to the medication—many people find it improves after a few weeks on the same dose.
- Nausea typically peaks within 2–3 days of an injection and may ease as the week progresses
- Eating smaller, lighter meals and staying hydrated can help reduce nausea severity
- Avoiding fatty, greasy, or strongly flavoured foods often helps
- Other common side effects include diarrhoea, constipation, vomiting, and stomach pain
- Most side effects are temporary and mild-to-moderate, but some people find them troublesome enough to consider stopping treatment
If nausea is severe or persistent beyond the first month, inform your prescriber—they may slow your dose increases or adjust your treatment plan. Serious side effects requiring urgent medical attention include severe stomach pain (possible pancreatitis), allergic reactions, or changes in vision.
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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.
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Accessing Mounjaro in the UK: NHS vs Private Routes & Costs
In the UK, Mounjaro is available through two routes: NHS specialist services and private online prescribing. NHS access is through tier 3 or tier 4 specialist weight management services—you'll need a GP referral and may wait months depending on your region. Private access is faster: you complete an online clinical assessment with a UK-licensed prescriber, receive a prescription if suitable, and collect from a GPhC-registered pharmacy.
Private costs typically range from £129–£320 per month depending on your dose. Doses start at 2.5 mg (lower cost) and escalate to 15 mg (maximum dose) over 5 months, so your monthly cost may increase. NHS costs are covered by the NHS if approved. Before starting any GLP-1 medication like tirzepatide, use our free GLP-1 weight loss calculator to estimate potential results and check your BMI with our free BMI calculator to see if you meet eligibility criteria (typically BMI 30+ or 27+ with health conditions).
- 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 Mounjaro nausea last?
Nausea usually peaks within 2–3 days of your weekly injection and may ease as the week progresses. For most people, nausea improves significantly after 2–4 weeks as your body adjusts. If nausea persists beyond the first month on the same dose, contact your prescriber to discuss whether continuing is right for you.
Is Mounjaro nausea dangerous?
Mild-to-moderate nausea is not dangerous, though it's uncomfortable. However, severe nausea causing vomiting, inability to eat, or dehydration should be reported to your prescriber. Severe stomach pain spreading to your back could indicate pancreatitis and requires urgent medical attention.
Can I take anti-nausea medication with Mounjaro?
Some anti-nausea medications may be suitable, but always check with your prescriber or GP before adding any new medication. Mounjaro slows stomach emptying, so some medications absorb differently. Your prescriber can advise which options are safe to combine with your tirzepatide treatment.
What's the difference between Mounjaro and Wegovy nausea?
Both are GLP-1-type medications causing similar side effects. Mounjaro is a dual GIP+GLP-1 agonist while Wegovy is GLP-1-only. Clinical trials suggest Mounjaro may achieve slightly greater weight loss, but nausea rates are comparable. Individual tolerance varies—some people tolerate one better than the other.
How much does private Mounjaro cost in the UK?
Private costs range from approximately £129–£320 per month depending on your dose. Starting doses (2.5–5 mg) are cheaper; maximum dose (15 mg) costs more. NHS costs are covered if approved through specialist services, though waiting times can be lengthy. Check our GLP-1 weight loss calculator to see if this treatment is likely to be cost-effective for your situation.
Ready to take control of your weight loss journey?
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