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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Mounjaro Headache — NHS Guidance for UK Users
Headaches can occur when taking Mounjaro (tirzepatide), though they're not among the most common side effects reported in UK clinical trials. If you're experiencing headaches whilst on this prescription weight management injection, it's important to understand what's happening, when they typically resolve, and when to contact your GP. This guide covers NHS guidance, what the evidence shows, and practical steps you can take.
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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.
Mounjaro and Headaches — What the Evidence Shows
Headaches are reported as a common side effect in clinical trials of Mounjaro (tirzepatide), though they affect a smaller proportion of users compared to nausea or stomach discomfort. In the SURMOUNT trials, headaches occurred in approximately 13% of participants taking the 15mg dose, making them less frequent than gastrointestinal effects but still notable.
Headaches may develop for several reasons: dehydration is a common trigger (GLP-1 medications can affect appetite and fluid intake), blood sugar changes during weight loss, or caffeine withdrawal if eating patterns have shifted. Some users report headaches during the dose-titration phase, which typically last a few days to a week as the body adjusts to the medication.
- Usually mild to moderate in intensity
- Often settle within the first 1–2 weeks of starting or increasing your dose
- More likely if dehydrated or skipping meals
- Contact your GP if severe or persistent beyond two weeks
Mounjaro's UK prescription eligibility requires a BMI of 30 or above, or 27 or above with weight-related health conditions—your GP or specialist can assess whether this medication is appropriate for you.
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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 — Practical Steps
Most Mounjaro-related headaches respond well to simple self-care measures. Ensure you're drinking enough water throughout the day—aim for 6–8 glasses—as dehydration is a frequent trigger during the early weeks of treatment. Eat small, regular meals even if your appetite is reduced, as skipping meals can lower blood sugar and cause headaches. If you normally drink caffeine, reduce intake gradually rather than stopping suddenly, as caffeine withdrawal headaches are common during lifestyle changes.
Over-the-counter pain relief like paracetamol is safe to use with Mounjaro, though check with your GP or pharmacist if you're taking other medications. Keep a simple log of when headaches occur and note any patterns—this helps your GP understand whether they're dose-related or linked to other factors. If headaches are severe, frequent, or accompanied by vision changes, weakness, or confusion, contact your GP promptly as these could indicate a more serious condition.
- 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 common are headaches with Mounjaro in the UK?
Headaches affect roughly 13% of users in clinical trials, making them a common but not very frequent side effect. Most users experience them during dose adjustments and they typically resolve within 1–2 weeks. Individual experiences vary widely.
Should I stop taking Mounjaro if I get a headache?
No—do not stop your Mounjaro without speaking to your GP. Most Mounjaro-related headaches are mild and temporary. Contact your prescriber if headaches are severe, persistent beyond two weeks, or accompanied by other concerning symptoms like vision changes.
Can I take paracetamol with Mounjaro?
Yes, paracetamol is safe to use with Mounjaro for headache relief. Always follow the dose instructions on the packet. If you're taking other medications, check with your GP or pharmacist first to ensure there are no interactions.
What should I do if headaches get worse on a higher Mounjaro dose?
Contact your GP or your specialist weight management service. They may recommend staying on your current dose longer before increasing, or investigate whether headaches are linked to dehydration, meal skipping, or caffeine changes rather than the medication itself.
When should I see my GP about Mounjaro headaches?
Contact your GP if headaches are severe, last longer than two weeks, or come with vision problems, weakness, confusion, or neck stiffness. These could indicate a separate medical issue. For mild headaches during dose adjustment, self-care usually helps—but your GP is always available to discuss concerns.
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