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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Why Does Mounjaro Cause Headaches?
Headaches are a reported side effect of Mounjaro (tirzepatide), though they affect only a small percentage of people taking this prescription-only weight management injection. Understanding why they occur, how common they are, and what you can do about them is important when considering this GLP-1 and GIP receptor agonist medication. This guide explains the mechanism, prevalence, and what to expect in the UK context.
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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.
How Mounjaro May Trigger Headaches
Headaches during Mounjaro treatment typically occur as your body adjusts to the medication during the initial weeks of treatment or when doses are increased. Several mechanisms may contribute: rapid changes in blood sugar levels can trigger tension headaches, particularly in people transitioning from higher blood sugar patterns; dehydration is common with Mounjaro due to nausea and reduced fluid intake, and dehydration is a well-known headache trigger; dose titration effects mean headaches often improve as your body adapts over weeks; and gastrointestinal changes including nausea and vomiting can indirectly cause tension headaches.
Clinical trial data shows headaches are reported in approximately 5–10% of people taking tirzepatide, making them less common than nausea or diarrhoea. Most headaches are mild to moderate and tend to resolve within the first few weeks of treatment or after dose adjustment. If headaches persist beyond this adjustment period, always discuss with your GP or the prescriber who issued your Mounjaro KwikPen prescription.
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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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Managing Mounjaro Headaches and UK Access Routes
Managing headaches: Stay hydrated by drinking regular water throughout the day, eat small regular meals to maintain stable blood sugar, take paracetamol or ibuprofen as directed on the packet, and ensure adequate sleep. Most importantly, inform your prescriber if headaches are severe, persistent beyond two weeks, or accompanied by vision changes, as these may indicate a different underlying issue.
In the UK, Mounjaro is accessible through two routes: NHS specialist weight management services (tier 3/4) via GP referral, where availability and waiting times vary significantly by region; and private online prescribing through GPhC-registered pharmacies following an online consultation with a UK-licensed prescriber. Private costs typically range from £180–£300+ per month depending on your dose. Always ensure any prescriber conducting your assessment is UK-licensed and registered.
Use our free GLP-1 weight loss calculator above to understand how Mounjaro may work for your individual situation, and consult our BMI calculator to see whether you meet the eligibility criteria (BMI 30+ or 27–29.9 with weight-related health conditions). When starting any weight loss medication, tracking your progress is valuable — our free progress tracker helps you monitor weight, symptoms, and side effects over time, which you can share with 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?
Headaches are reported in approximately 5–10% of people taking tirzepatide (Mounjaro) in clinical trials, making them less common than nausea or diarrhoea. Most are mild to moderate and tend to improve within the first few weeks as your body adjusts to the medication.
What should I do if I get a headache while taking Mounjaro?
Stay well-hydrated, eat regularly to maintain stable blood sugar, and take over-the-counter paracetamol or ibuprofen as directed. Most headaches resolve naturally. If headaches persist beyond two weeks, are severe, or are accompanied by vision changes, contact your GP or prescriber immediately.
How much does Mounjaro cost privately in the UK?
Private Mounjaro costs in the UK typically range from £180–£300+ per month depending on your dose level. Starting doses (2.5–5 mg) are usually cheaper than maximum doses (15 mg). Always check with the prescriber and pharmacy for exact pricing, as costs vary between providers.
Can I get Mounjaro through the NHS in the UK?
Yes, Mounjaro is available through NHS specialist weight management services (tier 3/4), but access is through GP referral and availability varies significantly by region. Waiting times can be several months to over a year in many areas. Private online prescribing offers faster access but requires payment.
Why do headaches often improve after the first few weeks of Mounjaro?
Headaches typically ease as your body adjusts to the medication, blood sugar stabilises, and you learn to manage hydration and nutrition. Additionally, dose titration is gradual — starting at 2.5 mg and increasing every 4 weeks — allowing your system to adapt progressively to each new dose level.
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.