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 vs Wegovy: Headaches and Side Effects
Headaches are a recognised but uncommon side effect of both Mounjaro (tirzepatide) and Wegovy (semaglutide). If you're considering either GLP-1 weight loss medication in the UK, understanding how side effects compare can help you make an informed decision with your prescriber. This guide explains headache incidence, severity, management strategies, and how the two medications differ in terms of overall tolerability based on clinical evidence and UK prescribing guidance.
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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.
Headaches: Mounjaro vs Wegovy Incidence
Mounjaro (tirzepatide) headaches are reported in clinical trials but are not listed as a "common" side effect (affecting more than 1 in 10 people). When headaches do occur with Mounjaro, they are typically mild to moderate and often resolve within the first few weeks as your body adjusts to each dose increase during dose titration.
Wegovy (semaglutide) headaches are similarly uncommon, reported in clinical trials at low frequencies. The STEP-1 trial showed headache incidence was comparable between active treatment and placebo groups, suggesting many reported headaches may not be directly caused by the medication.
Neither medication lists headache as a "very common" side effect. If headaches persist beyond the first 4 weeks after a dose increase, or are severe, discuss with your prescriber—other causes should be explored.
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Managing Headaches: UK Practical Guidance
If you experience headaches while taking Mounjaro or Wegovy, simple management strategies include staying well hydrated (dehydration is a common trigger), eating regular balanced meals, and ensuring adequate sleep. Over-the-counter painkillers like paracetamol are safe to use alongside both medications.
Headaches often improve once your body adapts to your current dose. If you're due for a dose increase with your Mounjaro KwikPen or Wegovy injection, discuss with your prescriber whether to delay escalation until headaches resolve. For UK NHS patients accessing these medications through specialist weight management services, or those using private UK prescription routes, your prescriber can adjust your dose schedule if needed.
- 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.
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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 more common with Mounjaro or Wegovy?
Headaches are uncommon with both medications and occur at similar rates. Clinical trial data shows headaches are not listed as a "common" side effect for either Mounjaro or Wegovy. If headaches develop, they typically occur during the first few weeks after starting or increasing your dose, then improve as your body adjusts. Always report persistent headaches to your prescriber.
How long do headaches last with Mounjaro?
Most headaches associated with Mounjaro resolve within 2–4 weeks of starting a new dose or increasing during dose titration. If headaches persist beyond this period or worsen, contact your prescriber. Staying hydrated, eating regular meals, and managing stress can help reduce headache frequency.
Can I take paracetamol with Mounjaro or Wegovy?
Yes, paracetamol is safe to take alongside both Mounjaro and Wegovy. Other over-the-counter painkillers like ibuprofen are also generally safe, but always check with your prescriber if you're taking other medications. Staying well hydrated and maintaining regular meal patterns may help prevent headaches occurring in the first place.
Should I stop my Mounjaro or Wegovy if I get headaches?
No—do not stop your medication without guidance from your prescriber. Headaches alone are not a reason to discontinue either medication. However, if you experience severe headaches, changes in vision, or headaches accompanied by other serious symptoms, contact your prescriber or GP immediately. They can assess whether the headaches are medication-related or caused by another condition.
Do headaches mean my UK prescription dose is too high?
Not necessarily. Headaches can occur at any dose and are typically related to your body's adjustment phase rather than the dose being unsuitable. Your prescriber will assess whether to maintain your current dose, delay dose escalation, or investigate other causes. NHS specialist services and private prescribers in the UK can adjust your Mounjaro or Wegovy schedule individually.
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