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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Light Headedness with Mounjaro vs Wegovy
Dizziness and light headedness can occur with both Mounjaro (tirzepatide) and Wegovy (semaglutide), but the frequency and underlying causes differ between these two weight management injections. Both are prescription-only GLP-1 (and in Mounjaro's case, dual GIP+GLP-1) receptor agonist medications licensed in the UK. Understanding why dizziness happens and how the medications compare can help you discuss side effects with your prescriber before starting treatment.
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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.
Why Dizziness Occurs — SURMOUNT vs STEP Trial Data
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist. In the SURMOUNT-1 clinical trial, dizziness was reported as a common side effect affecting up to 1 in 10 participants. Light headedness with Mounjaro typically occurs due to: rapid blood sugar changes (especially in those with type 2 diabetes), dehydration from nausea and reduced food intake, and slower stomach emptying affecting nutrient absorption. Starting at a low 2.5 mg dose helps minimise this.
Wegovy (semaglutide) is a GLP-1 agonist only — a single mechanism rather than dual. In the STEP-1 clinical trial, dizziness was also reported but slightly less frequently than with Mounjaro. The underlying causes are similar: appetite reduction leading to lower calorie intake, potential dehydration, and adjustments to how quickly your stomach processes food. Wegovy doses escalate more slowly (starting 0.25 mg), which some users find easier to tolerate.
- Both medications slow gastric emptying, which can affect blood sugar and electrolyte balance
- Lower food intake may reduce hydration and nutrient absorption
- Individual tolerance varies significantly based on starting dose and escalation pace
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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 Suitability
There is no definitive evidence that one medication is universally "better" for dizziness than the other — tolerance is highly individual. However, some users report fewer dizzy spells with Wegovy's slower dose escalation schedule, whilst others find Mounjaro's dual mechanism easier once they adapt. Your prescriber will assess which is more suitable based on your: medical history (especially diabetes or blood pressure medication use), previous medication tolerances, and individual risk factors.
If dizziness develops, practical steps include: staying well hydrated, eating small balanced meals even if not hungry, avoiding sudden position changes, and monitoring blood pressure at home if possible. Using our free BMI calculator and GLP-1 weight loss calculator can help track your baseline health metrics before starting either medication, providing context for your prescriber during the clinical assessment.
- 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 dizziness a common side effect of Mounjaro in the UK?
Yes, dizziness was reported in clinical trials as a common side effect affecting up to 1 in 10 Mounjaro users. It typically occurs in the first few weeks as your body adjusts. Most cases resolve as you adapt to the medication and maintain proper hydration. Always inform your prescriber if dizziness is severe or persistent.
Does Wegovy cause less dizziness than Mounjaro?
Clinical trial data suggests dizziness may be slightly less frequent with Wegovy, though individual experiences vary widely. Wegovy's slower dose escalation (starting 0.25 mg) may help some people tolerate it better. Your prescriber can discuss which medication suits your specific health profile during your clinical assessment.
What should I do if I feel dizzy on Mounjaro?
Stay hydrated by drinking water regularly, eat small balanced meals, avoid standing up too quickly, and rest if needed. Check your blood pressure if possible. Contact your GP if dizziness is severe, persistent, or accompanied by chest pain, changes in vision, or fainting. Never stop the medication without medical guidance.
Can I switch from Mounjaro to Wegovy if dizziness is severe?
Possibly, but any medication switch must be managed by your prescriber. Switching requires time to clear one medication before starting another. Your prescriber will assess whether the dizziness is likely to improve with continued use or if an alternative is genuinely needed based on your clinical picture.
Is light headedness worse at higher Mounjaro doses?
Not necessarily. Some people experience more dizziness at higher doses, whilst others feel better once fully adjusted. The 15 mg maximum dose is reached gradually over 20+ weeks, allowing your body to adapt. Starting low and titrating slowly is the standard approach to minimise dizziness risk.
Ready to take control of your weight loss journey?
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