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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Headaches with Mounjaro — What You Need to Know
Headaches are a reported side effect of Mounjaro (tirzepatide) in some people using this prescription weight management injection. While not everyone experiences headaches, understanding why they occur, how long they typically last, and when to seek medical advice can help you manage this side effect effectively. This guide explains what NHS guidance and clinical data tell us about headaches during Mounjaro treatment, alongside practical management strategies. If you're considering this medication or already taking it, MyWeightCheck's free tools can help you track your weight progress and overall health alongside medical care.
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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.
Why Headaches Occur on Mounjaro Treatment
Headaches may develop when starting Mounjaro or during dose titration because the medication affects how your body processes glucose and regulates hormones. Tirzepatide, the active ingredient in Mounjaro delivered via the KwikPen device, is a dual GIP and GLP-1 receptor agonist — meaning it influences multiple hormone pathways simultaneously. This can trigger headaches in some people, particularly during the first few weeks of treatment or when increasing doses.
Headaches are classified as common side effects according to UK prescribing information, meaning they may affect up to 1 in 10 people. The headaches are typically mild to moderate and often improve as your body adjusts to the medication. Dehydration, changes in eating patterns, and blood sugar fluctuations can also contribute. Your prescriber should have discussed potential side effects before starting treatment, and this is information you can revisit at any time.
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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 Headaches & When to Contact Your GP
If you develop headaches while taking Mounjaro, several practical steps may help: stay well hydrated by drinking plenty of water throughout the day, eat regular balanced meals to maintain stable blood sugar, ensure adequate rest, and consider over-the-counter pain relief such as paracetamol if needed. Keep a simple record of when headaches occur — before, during, or after your weekly injection — to identify patterns and share with your healthcare provider.
Contact your GP if headaches are severe, persistent, or worsening, or if they occur alongside other concerning symptoms such as vision changes, dizziness, or unusually high blood pressure. Your prescriber may recommend dose adjustment, temporary pausing of treatment, or alternative GLP-1 medications such as Wegovy. Never stop taking Mounjaro without medical guidance. Your individual eligibility for continued treatment and any adjustments should always be assessed by your prescriber.
- 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.
Are headaches a common side effect of Mounjaro?
Yes, headaches are classified as a common side effect of Mounjaro and may affect up to 1 in 10 people. They typically occur during the first few weeks of treatment or during dose titration phases. Most headaches are mild to moderate and often improve as your body adjusts to the medication. Always discuss any concerning symptoms with your GP or prescriber.
How long do Mounjaro headaches usually last?
Headaches often improve within the first 1–2 weeks as your body adjusts to tirzepatide. However, duration varies between individuals. Some people experience no headaches at all, while others may have intermittent mild headaches throughout treatment. If headaches persist beyond 2–3 weeks or worsen, contact your prescriber for personalised guidance.
Can I take paracetamol alongside Mounjaro?
Over-the-counter paracetamol is generally safe to take alongside Mounjaro, but always inform your prescriber of any medications or supplements you're using. They can confirm there are no interactions with your individual health profile. If you're taking other medications, ask your GP before adding any new pain relief.
What should I do if headaches are severe on Mounjaro?
Contact your GP or prescriber immediately if headaches are severe, persistent, or accompanied by other symptoms such as vision changes, dizziness, or chest pain. Your prescriber may recommend dose adjustment, temporary cessation, or a different weight management option. NHS guidance supports discussing all concerns with your healthcare provider.
Is Mounjaro the only weight loss injection that causes headaches?
Headaches can occur with other GLP-1 medications such as Wegovy (semaglutide) and Saxenda (liraglutide), though individual experiences vary. Your prescriber can discuss how different medications may affect you personally. MyWeightCheck's free tools help you track how you feel during treatment alongside your medical care.
Ready to take control of your weight loss journey?
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