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 — What You Need to Know
Feeling light headed whilst taking Mounjaro is a recognised side effect that some people experience, though it's not among the most common. Dizziness can occur for several reasons related to how tirzepatide works in your body — including changes in blood sugar levels, dehydration, or rapid stomach emptying. If you're experiencing light headedness on your Mounjaro KwikPen injections, it's important to understand whether it's expected, when to seek help from your GP, and what 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 Mounjaro May Cause Dizziness
Dizziness on Mounjaro can occur through several mechanisms. Tirzepatide slows how quickly food leaves your stomach (gastric emptying), which can sometimes lead to changes in blood sugar levels and fluid shifts. This may temporarily lower your blood pressure, causing light headedness or dizziness — particularly when standing up quickly. Additionally, if you're eating less due to reduced appetite, you may not be consuming enough calories or electrolytes, both of which can contribute to dizziness. Some people also experience nausea alongside dizziness, which compounds the effect. Dehydration is another common cause — GLP-1 medications can increase fluid loss, so maintaining hydration is essential. Finally, if you have type 2 diabetes and are also taking insulin or other diabetes medications, Mounjaro can interact with these, affecting blood sugar control and potentially causing dizziness.
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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 Light Headedness Is Concerning and What to Do
Mild, occasional dizziness may be expected during dose adjustment phases, but you should contact your GP if dizziness is severe, persistent, or accompanied by other symptoms such as chest pain, shortness of breath, fainting, or confusion. Your GP may want to check your blood pressure, blood sugar levels, and overall hydration status. If you feel faint, sit or lie down immediately to prevent falls and injury. It's worth keeping a symptom diary — note when dizziness occurs, how long it lasts, and what you were doing. This information helps your GP assess whether the dizziness is related to Mounjaro dose, your other medications, eating patterns, or an unrelated health issue. Never stop taking Mounjaro without discussing it with your prescriber first.
- 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?
Dizziness is recognised as a possible side effect but is not listed as very common or common in clinical trials. It's less frequent than nausea, vomiting, or stomach pain. If you experience it, it doesn't necessarily mean something is wrong — but it's worth monitoring and reporting to your GP.
How can I reduce light headedness whilst taking Mounjaro?
Stay well hydrated by drinking plenty of water throughout the day. Eat small, regular meals even if your appetite is reduced — undereating can cause dizziness. Rise slowly from sitting or lying down to avoid sudden blood pressure drops. Avoid standing for long periods. If you feel faint, sit down immediately. Your GP can also check whether other medications are contributing.
Could Mounjaro be affecting my diabetes medications and causing dizziness?
Yes, tirzepatide can affect how your body processes blood sugar, potentially requiring adjustments to insulin or other diabetes medications. If you take diabetes treatment and experience new dizziness on Mounjaro, inform your prescriber — they may need to adjust your diabetes medication doses to prevent low blood sugar (hypoglycaemia).
Should I stop taking Mounjaro if I feel light headed?
Don't stop Mounjaro without speaking to your GP or prescriber first. Stopping suddenly isn't advisable. Instead, contact your healthcare provider to discuss your symptoms. They can assess whether the dizziness is related to Mounjaro, your dose, dose titration timing, other medications, or lifestyle factors — and advise next steps.
How does Mounjaro's dose titration schedule affect dizziness?
During dose escalation phases (when your Mounjaro dose increases every 4 weeks), your body is adjusting to stronger effects on appetite and gastric emptying. Dizziness may be more noticeable when you first move to a new dose. This typically settles within a week or two. If it persists, discuss with your prescriber — they may slow your dose escalation or investigate other causes.
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.