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
Lightheaded on Mounjaro — What You Need to Know
Feeling lightheaded or dizzy whilst taking Mounjaro (tirzepatide) is a relatively common side effect, particularly during the dose titration phase when your body is adjusting to the medication. Dizziness may occur for several reasons, including changes in blood pressure, dehydration, or reduced food intake. Understanding what causes this symptom and when it requires medical attention can help you manage your treatment safely. If you experience persistent or severe dizziness, always contact your GP or the prescriber who issued your Mounjaro KwikPen prescription for personalised advice.
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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.
Common Causes of Lightheadedness on Mounjaro
Lightheadedness whilst taking Mounjaro can stem from several factors linked to how the medication works. Reduced appetite and food intake is a primary cause — Mounjaro slows gastric emptying and reduces hunger signals, which may lead to eating significantly less. If you're not consuming enough calories or staying hydrated, dizziness can result. Blood pressure changes are also documented; some people experience temporary drops in blood pressure as their body adjusts to the medication. Dehydration is particularly common, as nausea and vomiting — very common side effects during the initial weeks — can reduce fluid intake. Additionally, dose adjustment phases may trigger dizziness as your body acclimates. Most cases of lightheadedness are mild and transient, resolving as you progress through dose titration or as your body adapts. However, persistent or worsening dizziness should always be reported to your prescriber or GP.
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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.
When to Seek Medical Advice
Contact your GP or prescriber urgently if lightheadedness is severe, persistent, or accompanied by other concerning symptoms such as chest pain, shortness of breath, fainting, or severe headache. These could indicate a more serious condition requiring immediate evaluation. Mild, occasional dizziness that resolves within a few minutes is usually not cause for alarm, particularly during the first few weeks of treatment. However, if dizziness significantly impacts your daily life or interferes with driving, you should discuss this with your healthcare provider. They may adjust your dose, recommend dietary or hydration strategies, or prescribe supportive treatment. Never drive or operate machinery if you feel lightheaded — safety is paramount. Your GP can assess your individual situation and determine whether continuing Mounjaro is appropriate or if an alternative weight management approach would be better suited to you.
- 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 lightheadedness a common side effect of Mounjaro?
Yes, dizziness is listed as a common side effect affecting up to 1 in 10 people taking Mounjaro. It's often temporary and tends to improve as your body adjusts during dose titration. Most cases resolve within the first few weeks of treatment.
What should I do if I feel lightheaded whilst taking Mounjaro?
Sit or lie down immediately to prevent falls. Drink water and eat a small, balanced snack if you can tolerate it. Rest until the dizziness passes. If it persists or worsens, contact your GP or the prescriber who issued your prescription for guidance.
Can dehydration cause lightheadedness on Mounjaro?
Yes, dehydration is a common trigger. Mounjaro's side effects like nausea and vomiting can reduce fluid intake. Aim to drink water consistently throughout the day, even if you're not eating much. Proper hydration often reduces dizziness significantly.
Should I stop taking Mounjaro if I feel lightheaded?
Don't stop without medical guidance. Contact your prescriber or GP first to discuss your symptoms. They may recommend dose adjustments, dietary changes, or other management strategies before deciding whether to continue or switch treatments.
Can low blood sugar cause lightheadedness on Mounjaro?
Low blood sugar is more common if you're also taking diabetes medications like insulin or sulphonylureas. If you have diabetes, monitor your blood sugar regularly and inform your GP if dizziness coincides with low readings — medication adjustments may be needed.
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.