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
Free tracker included with every download this week
Feeling Light Headed on Mounjaro — What You Need to Know
Feeling light headed or dizzy on Mounjaro (tirzepatide) is not uncommon, though it's not listed as a very common side effect in clinical trials. This sensation may occur due to several factors related to how Mounjaro works in your body — including changes in blood pressure, reduced food intake, dehydration, or adjustments to your medication dose. Understanding why this happens and when to contact your GP is important for managing your weight loss journey safely. This guide covers the causes, when to seek medical advice, and practical steps to manage dizziness whilst on tirzepatide.
10,000+ calculations today · NHS-aligned thresholds · 100% free
Calculate Your BMI Instantly
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 Mounjaro Might Cause Light Headedness
Light headedness on Mounjaro can result from several interconnected factors. Blood pressure changes: Mounjaro is a dual GIP and GLP-1 receptor agonist that affects how your body regulates blood sugar and appetite. As you lose weight, your blood pressure may drop, which can trigger dizziness — particularly when standing up quickly (orthostatic hypotension). Reduced calorie intake: Mounjaro suppresses appetite effectively, meaning you eat less. If your food intake drops too far or you're not eating balanced meals, blood sugar can dip, causing lightheadedness. Dehydration: Many people on Mounjaro experience nausea, vomiting, or diarrhoea — all of which increase fluid loss. Dehydration is a common and easily reversible cause of dizziness. Dose adjustments: When starting Mounjaro or increasing from 2.5 mg to 5 mg, 7.5 mg, or higher doses, your body is adjusting to stronger hormone signalling. This transition period may temporarily trigger dizziness. Blood sugar regulation: If you're also taking diabetes medication (insulin or sulphonylureas), Mounjaro's blood sugar-lowering effects combined with your medication may cause hypoglycaemia (low blood sugar), which causes dizziness and shakiness.
Clinically BackedWeight Loss
No appointments. No waiting rooms. Just care — from a UK-regulated online pharmacy.
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.
When to Contact Your GP and What to Do
Contact your GP immediately if dizziness is severe, persistent, or accompanied by chest pain, shortness of breath, fainting, or vision changes — these could indicate a more serious issue requiring urgent assessment. Seek routine GP advice if light headedness continues beyond a few days after a dose increase, or if it's affecting your daily activities or ability to work safely.
Practical steps to manage dizziness: Drink plenty of water throughout the day — aim for at least 2 litres daily to counter dehydration from nausea or diarrhoea. Eat regular, balanced meals with protein and complex carbohydrates to stabilise blood sugar — even if appetite is suppressed, small frequent meals are better than skipping food. Stand up slowly from sitting or lying down, especially in the morning, to allow blood pressure to adjust. If you're taking insulin or sulphonylureas, discuss with your prescriber about dose adjustments, as Mounjaro's effects may require medication changes. Keep a simple symptom diary — note when dizziness occurs, what you've eaten, your activity level, and the Mounjaro dose you're on. Share this with your GP to identify patterns.
- 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 light headedness a common side effect of Mounjaro?
Light headedness is not listed as a very common side effect in clinical trials. However, it can occur due to blood pressure changes, dehydration, reduced food intake, or dose adjustments. If you experience dizziness, contact your GP to rule out other causes and ensure you're managing your dose safely.
Could my light headedness be low blood sugar from Mounjaro?
Yes, particularly if you're also taking diabetes medication like insulin or sulphonylureas. Mounjaro lowers blood sugar, and combined with other diabetes drugs, this can cause hypoglycaemia (low blood sugar), which triggers dizziness, shakiness, and sweating. Your prescriber may need to adjust your diabetes medication dose.
How can I prevent dizziness when starting Mounjaro?
Stay well hydrated by drinking 2+ litres of water daily. Eat regular balanced meals even if appetite is suppressed — blood sugar crashes from undereating cause dizziness. Stand up slowly to avoid sudden blood pressure drops. If nausea or diarrhoea is severe, contact your prescriber, as these can cause dehydration and lightheadedness.
Should I stop taking Mounjaro if I feel light headed?
Do not stop suddenly without talking to your prescriber. Some dizziness is temporary during dose adjustments and settles within days. However, if it's severe or persistent, contact your GP or prescriber for guidance — they may adjust your dose, medication timing, or food intake strategy rather than stopping treatment entirely.
How long does Mounjaro dizziness typically last?
Mild dizziness during dose increases often resolves within 2–7 days as your body adjusts. If it persists beyond a week or worsens, this suggests an underlying cause like dehydration, undereating, or low blood sugar that needs addressing. Keep your GP informed so they can investigate further.
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.