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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Does Mounjaro Cause Migraines?
Mounjaro (tirzepatide) is a prescription-only weight management injection licensed in the UK. Headaches and migraines are not listed as common side effects in clinical trials, though some people do report head discomfort when starting treatment. Understanding the difference between typical adjustment headaches and concerning migraines is important. If you're considering Mounjaro or currently taking it, knowing what to expect helps you make informed decisions about your health. This guide covers what the evidence shows about Mounjaro and migraines, when to seek GP advice, and how it compares to other GLP-1 medications like Wegovy.
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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.
Headaches and Mounjaro — What the Evidence Shows
Headaches are not listed as a common side effect in the SURMOUNT clinical trials for Mounjaro (tirzepatide). The most frequently reported side effects are gastrointestinal — nausea, diarrhoea, vomiting, and constipation. However, headaches can occur during the adjustment period when starting any new medication, particularly during the first few weeks or when your dose increases.
Some people report mild to moderate headaches when beginning Mounjaro, especially if they experience significant nausea or dehydration. These are typically temporary adjustment reactions rather than true migraines. True migraines — characterised by severe throbbing pain, often on one side of the head, sometimes with light sensitivity or nausea — are uncommon but have been reported by individual users.
- Adjustment headaches often improve within days to weeks as your body adapts
- Staying hydrated helps minimise headache risk during dose titration
- Dehydration from gastrointestinal side effects can trigger or worsen headaches
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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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When to Contact Your GP About Mounjaro Headaches
Contact your GP if you experience severe, persistent, or worsening headaches whilst taking Mounjaro, especially if they differ from headaches you've had before. Seek urgent medical attention if a headache is accompanied by vision changes, chest pain, severe stomach pain, or signs of a serious allergic reaction.
Your GP can assess whether your headaches are related to Mounjaro, dehydration, dose adjustment, or an unrelated issue. They may recommend hydration strategies, timing of doses, or adjustments to your treatment plan. If migraines become problematic, your prescriber might slow your dose titration or explore alternative weight management options. Calculate your personal BMI using our free BMI calculator to discuss your overall weight management strategy with your healthcare team.
- 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 migraine a common side effect of Mounjaro?
No. Headaches are not listed as a common side effect in clinical trials. Migraines specifically are uncommon. Some people report mild adjustment headaches in the first weeks, usually linked to nausea or dehydration rather than the medication itself. True migraines are rare but possible.
Can Mounjaro trigger migraines in people who don't normally get them?
It's possible but uncommon. Mounjaro doesn't directly cause migraines in most people. If headaches develop, they're typically mild adjustment reactions. However, if you have a personal or family history of migraines, mention this to your prescriber before starting treatment so they can monitor you appropriately.
How can I reduce headache risk when starting Mounjaro?
Stay well hydrated — drink plenty of water throughout the day. Manage nausea with small, frequent meals and avoid triggers. Take your injection at a consistent time each week. If headaches occur during dose titration, inform your prescriber; they may adjust your schedule. Most adjustment headaches improve naturally within 1–2 weeks.
Should I stop Mounjaro if I develop migraines?
Don't stop without contacting your GP or prescriber first. Most headaches during Mounjaro treatment are temporary and manageable. Your prescriber can assess whether your migraines are related to the medication or another cause, and discuss options — which may include continuing with hydration support or exploring alternatives like Wegovy.
Does Wegovy cause migraines less frequently than Mounjaro?
Both Mounjaro and Wegovy rarely list migraines as a common side effect. Wegovy (semaglutide) is a single GLP-1 agonist, whilst Mounjaro is a dual GIP/GLP-1 agonist, but headache profiles are similar. Individual responses vary. Discuss your migraine history with your prescriber to choose the most suitable UK prescription option.
Ready to take control of your weight loss journey?
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