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 Light Headedness vs Wegovy — What's the Difference?
Feeling light headed (dizziness) is a reported side effect that some people experience when taking Mounjaro or other GLP-1 medications for weight management. Both Mounjaro (tirzepatide) and Wegovy (semaglutide) can cause dizziness as they work to regulate appetite and blood sugar levels. Understanding how these two prescription-only injections compare — and when to contact your GP — is important for safe use in the UK.
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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.
How Mounjaro and Wegovy Cause Light Headedness — Clinical Context
Dizziness on GLP-1 medications typically occurs during the first few weeks of treatment or after dose increases, and is reported in clinical trials for both drugs. The mechanism differs slightly between them:
- Mounjaro (tirzepatide) activates both GIP and GLP-1 receptors — a dual mechanism that may cause dizziness in 5–10% of users during dose titration, based on SURMOUNT trial data.
- Wegovy (semaglutide) activates GLP-1 receptors only — dizziness was reported in approximately 8% of trial participants, primarily during initial dose escalation.
Both medications slow gastric emptying (how quickly food leaves the stomach), which can reduce blood pressure slightly and contribute to dizziness, especially if you're not eating enough calories alongside the injection. This effect typically diminishes after the first 4–8 weeks as your body adjusts.
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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.
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Which Is More Likely to Cause Dizziness — Individual Factors Matter
Clinical trial data suggests dizziness rates are broadly similar between Mounjaro and Wegovy, but individual experience varies significantly. Your GP or prescriber will assess whether either medication is suitable for you based on your personal health history, current medications, and other side effect risk factors. Factors that may increase dizziness risk include dehydration, skipping meals, low blood pressure, or taking certain blood pressure medications. Using our free BMI calculator and GLP-1 weight loss calculator can help you understand your starting point and projected weight loss — information worth discussing with your prescriber when assessing side effect tolerability.
- 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 common on Mounjaro?
Dizziness is reported in approximately 5–10% of Mounjaro users, particularly during the first 4 weeks or after dose increases. It usually improves as your body adjusts. If dizziness persists or worsens, contact your GP — do not stop the injection without medical guidance.
Does Wegovy cause less dizziness than Mounjaro?
Clinical trials show similar dizziness rates between both medications (around 8% for Wegovy). Individual responses vary. Dizziness is typically temporary and related to dose titration rather than one drug being inherently "better" than the other.
What should I do if I feel light headed on my Mounjaro injection?
Ensure you're eating enough calories, staying hydrated, and having regular meals. Light headedness often resolves within days. Contact your GP if it persists beyond a week, you experience fainting, chest pain, or rapid heartbeat — these warrant urgent medical review.
Can I switch from Mounjaro to Wegovy if I get dizziness?
Switching medications requires a prescriber's decision. Dizziness on Mounjaro may resolve simply by waiting, adjusting meal timing, or staying hydrated — it's not always necessary to switch. Your GP can advise whether a switch is appropriate for you.
Is dizziness a sign the medication isn't working?
No. Dizziness during dose titration doesn't indicate the medication is ineffective — it's a temporary adjustment side effect. Clinical trials showed both Mounjaro and Wegovy are effective for weight management, with average weight loss of 15–21% over 68 weeks.
Ready to take control of your weight loss journey?
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