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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Headache From Mounjaro — What You Need to Know
Headaches are a commonly reported side effect when starting tirzepatide (Mounjaro), the UK prescription weight management injection. In clinical trials and real-world use, some people experience headaches during the initial weeks of treatment, particularly during dose titration. Understanding why this happens, how to manage it, and what your access options are in the UK can help you make informed decisions about this medication alongside a reduced-calorie diet and increased physical activity.
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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.
What Causes Headaches on Mounjaro — And How to Manage Them
Headaches when starting Mounjaro are thought to occur for several reasons. As your body adjusts to the dual GIP and GLP-1 receptor agonist effects, you may experience changes in blood sugar levels, altered eating patterns, or mild dehydration—all of which can trigger headaches. During dose titration (the gradual increase from 2.5 mg to your maintenance dose), headaches tend to be most noticeable in weeks 1–8, though they typically improve as your body adapts.
Managing Mounjaro-related headaches:
- Stay well hydrated—drink extra water throughout the day
- Eat regular, balanced meals to avoid blood sugar dips
- Rest and avoid stressful situations when possible
- Over-the-counter paracetamol or ibuprofen may help (check with your prescriber first)
- Keep a headache diary to track triggers and timing
If headaches are severe, persistent, or worsening, contact your prescriber. Most people find headaches resolve within the first 2–4 weeks as their body adjusts to the medication.
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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.
Accessing Mounjaro in the UK — Cost, NHS, and Private Routes
In the UK, Mounjaro is accessed through two main routes: NHS specialist services or private prescription. NHS access requires a referral to a tier 3 weight management service from your GP; availability and waiting times vary significantly by region and local integrated care board (ICB) decisions. NICE has approved tirzepatide for use within specialist NHS services, though access remains limited in many areas.
Private prescription route: You can obtain a prescription through a UK-licensed online prescriber following a clinical assessment. Private costs typically range from £150–£320 monthly depending on your dose. A GPhC-registered pharmacy dispenses your KwikPen. This route offers faster access without NHS waiting lists but requires meeting the same clinical eligibility criteria (BMI ≥30, or BMI 27–29.9 with weight-related health conditions). Try our free GLP-1 weight loss calculator to explore projected outcomes at different doses.
When comparing your options: Both NHS and private routes require a clinical assessment confirming you meet eligibility criteria. Your prescriber will discuss whether Mounjaro is suitable given your medical history, current medications, and weight management goals. Our BMI calculator can help you understand your current health baseline before starting any treatment. Storage is straightforward—unopened pens stay refrigerated at 2–8°C, and after first use you have 30 days at room temperature. If you switch between Mounjaro and Wegovy (semaglutide), your prescriber will guide the transition; approximate equivalence exists but individual adjustments are always necessary.
- 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 a headache a common side effect of Mounjaro?
Yes, headaches are reported as common side effects in clinical trials and real-world use, particularly during dose titration weeks 1–8. Most people find they resolve as their body adjusts. If headaches persist or worsen, discuss with your prescriber—it may indicate you need dose adjustment or additional support.
Can I buy Mounjaro on the NHS, or must I go private?
Mounjaro is available on the NHS through specialist tier 3 weight management services following a GP referral. However, NHS access is limited and varies by region—waiting lists can be lengthy. Private prescription is faster but costs £150–£320 monthly. Both routes require clinical assessment and eligibility confirmation (BMI ≥30 or 27–29.9 with comorbidities).
What's the difference between NHS and private Mounjaro prescription costs?
NHS prescription is free at the point of use if approved by your local specialist service. Private prescription typically costs £150–£320 monthly depending on your dose level. Private access is faster but requires upfront payment. Cost varies between providers—always check what's included (consultation, prescription, pharmacy fee).
How long does it take to access Mounjaro privately in the UK?
Private access is typically much faster than NHS. After booking an online consultation, you usually have a clinical assessment within 24–48 hours. If approved, your prescription is sent to a pharmacy within hours, and your KwikPen can arrive within 2–7 working days depending on the provider.
Will my headache on Mounjaro go away, or should I stop taking it?
Headaches usually resolve within 2–4 weeks as your body adjusts. Do not stop taking Mounjaro without speaking to your prescriber. If headaches are severe or accompanied by other concerning symptoms, contact them immediately. Many headaches can be managed with hydration, regular meals, and rest while your body adapts to the medication.
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.