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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Is Light Headedness a Side Effect of Mounjaro?
Light headedness can occur when taking Mounjaro (tirzepatide), though it is not listed as a very common side effect. It may develop due to several factors related to how the medication works, including changes in blood pressure, reduced food intake, or dehydration. If you experience persistent or severe light headedness while taking Mounjaro, it is important to contact your GP or prescriber. This guide explains what causes this symptom, when it becomes concerning, and practical steps you can take to manage it safely.
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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.
Why Does Mounjaro Cause Light Headedness?
Light headedness on Mounjaro can happen for several interconnected reasons. First, blood pressure changes — tirzepatide can affect heart rate and blood pressure regulation, particularly during dose escalation or when the body is adjusting to the medication. Second, reduced calorie intake — Mounjaro reduces appetite so significantly that some people eat considerably less than before. Without enough food, blood sugar can dip and blood pressure may drop, causing dizziness. Third, dehydration — nausea and vomiting (common early side effects) lead to fluid loss. Fourth, electrolyte imbalance — prolonged nausea or changes in eating patterns can deplete sodium and potassium, both essential for blood pressure stability. Finally, light headedness may indicate low blood sugar (hypoglycaemia), especially if you also take diabetes medication like insulin or a sulphonylurea. Your prescriber will have assessed your risk factors when issuing your Mounjaro KwikPen prescription, but if symptoms develop, report them promptly.
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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
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When to Seek Medical Advice
Contact your GP immediately if light headedness is severe, persistent, or accompanied by chest pain, shortness of breath, fainting, or confusion. These may indicate a serious condition requiring urgent assessment. Also seek medical advice if light headedness continues after the first few weeks or worsens with each dose increase. Mild, occasional light headedness that improves with hydration or eating something small may resolve naturally as your body adjusts. However, do not assume any symptom is harmless — your GP can check your blood pressure, heart rate, and blood glucose to rule out complications. If you take diabetes medication alongside Mounjaro, inform your prescriber, as dose adjustments may be needed. Keep a symptom diary noting when dizziness occurs, what you were doing, and what helps — this information helps your GP provide better support.
- 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.
Can I take paracetamol for light headedness from Mounjaro?
Paracetamol will not address the underlying cause of Mounjaro-related light headedness. Focus on hydration, eating regular small meals, and avoiding rapid position changes instead. If symptoms persist, contact your GP rather than relying on painkillers.
Does light headedness mean Mounjaro is not working?
No. Light headedness is a side effect unrelated to the medication's weight loss effectiveness. Many people experience both weight loss and temporary side effects. However, if the symptom is severe or distressing, discuss with your prescriber whether continuing at your current dose is appropriate.
Should I stop taking Mounjaro if I feel light headed?
Do not stop Mounjaro suddenly without medical advice, as this can cause other complications. Instead, contact your prescriber or GP immediately. They may advise staying at your current dose longer, delaying your next dose increase, or adjusting other medications you take.
How long does Mounjaro light headedness typically last?
For many people, light headedness improves within the first 2–4 weeks as the body adjusts. However, if it persists beyond this timeframe or emerges during dose escalation, it warrants medical assessment. Everyone responds differently, so timelines vary.
Can dehydration really cause light headedness on Mounjaro?
Yes, absolutely. Mounjaro reduces appetite and thirst signals, so you may drink less without realising. Aim for 2–3 litres of water daily, especially in the first few weeks. Dehydration is easily corrected and often resolves dizziness quickly.
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.