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 reported as a common side effect when starting Mounjaro (tirzepatide) for weight management in the UK. Most headaches occur during the initial dose titration phase and often improve as your body adjusts to the medication. If you're considering Mounjaro through NHS specialist services or exploring your options, it's important to understand what to expect, how headaches are managed, and when to contact your healthcare team. This guide covers NHS-specific guidance and practical information for UK adults.
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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.
NHS Eligibility and Mounjaro Prescription in the UK
Mounjaro is available through NHS specialist weight management services for adults who meet specific criteria. You must have a BMI of 30 kg/m² or above, or 27–29.9 kg/m² with at least one weight-related health condition including type 2 diabetes, high blood pressure, or cardiovascular disease. For adults of South Asian, Chinese, Black African, or Black Caribbean heritage, lower thresholds may apply — eligibility may start at BMI 27.5 or above.
Access is through NICE-approved tier 3 specialist services, typically following referral from your GP. Your prescriber will conduct a full clinical assessment before initiating treatment. During this assessment, any existing headache conditions or migraine history will be reviewed. The dose titration schedule — starting at 2.5 mg and increasing by 2.5 mg every 4 weeks up to 15 mg — is designed to help your body adjust gradually, which may reduce the likelihood of headaches developing.
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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.
Free Weight Loss Tools & Guides
Everything you need to understand your weight, explore medication options, and track your progress — completely free.
NHS vs Private Access and Headache Management
NHS specialist services provide comprehensive support during your treatment, including monitoring for side effects like headaches throughout your dose titration journey. However, NHS waiting lists can be lengthy in many regions — sometimes several months to over a year depending on your area's integrated care board (ICB) capacity.
Private online prescribing offers faster access without NHS referral requirements. A UK-licensed prescriber conducts a clinical assessment via online consultation, and if appropriate, issues a prescription dispensed by a GPhC-registered pharmacy. Both routes require the same clinical eligibility checks. If headaches develop with either NHS or private Mounjaro, you should report them to your prescriber so your KwikPen dose or titration schedule can be reviewed. Most headaches respond well to dose adjustment or resolve naturally within the first few weeks.
- 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 headache a common side effect of Mounjaro tirzepatide?
Yes, headache is reported as a common side effect affecting up to 1 in 10 people taking Mounjaro. It typically occurs during the initial dose titration phase and often improves as your body adjusts. Most headaches are mild to moderate and do not require stopping treatment.
How do I access Mounjaro through NHS services in the UK?
Ask your GP for a referral to your local tier 3 specialist weight management service. You must meet NICE eligibility criteria: BMI 30 or above, or 27–29.9 with weight-related health conditions. NHS services conduct a full clinical assessment including headache history before prescribing.
Should I stop Mounjaro if I develop a headache?
No — do not stop without speaking to your prescriber first. Most Mounjaro-related headaches improve within the first few weeks or resolve after dose adjustment. Contact your healthcare team to discuss symptoms; they may slow your dose titration or recommend over-the-counter pain relief.
What's the difference between NHS and private Mounjaro in terms of side effect monitoring?
Both require clinical assessment. NHS specialist services provide ongoing support through the health service; private prescribing offers faster access. Either way, report headaches to your prescriber so they can adjust your treatment plan if needed.
Can headaches during Mounjaro dose titration mean the medication isn't right for me?
Not necessarily. Headaches are a known temporary side effect and do not indicate the medication is unsuitable. Your prescriber may recommend slowing your dose titration, adjusting the timing of your KwikPen injection, or ensuring you're hydrated and eating regular meals — all of which can help reduce headache severity.
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.