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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Dizziness on Mounjaro vs Wegovy — What You Need to Know
Dizziness can occur with both Mounjaro (tirzepatide) and Wegovy (semaglutide) weight loss injections, though it's not listed as a common side effect for either medication. If you're experiencing dizziness whilst taking a GLP-1 or dual GIP and GLP-1 receptor agonist, it may be related to other factors such as changes in blood sugar, dehydration, rapid blood pressure changes, or dose adjustments. Both medications are prescribed following clinical assessment through the NHS or private providers in the UK. Understanding how each works and comparing their side effect profiles can help you discuss any symptoms with your GP or prescriber.
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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.
Mounjaro vs Wegovy — Mechanism and Side Effect Differences
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist manufactured by Eli Lilly, available in the UK as a once-weekly KwikPen injection. In the SURMOUNT-1 clinical trial, participants reported common side effects including nausea, diarrhoea, and abdominal pain, with fewer reports of dizziness. Wegovy (semaglutide) is a GLP-1-only agonist from Novo Nordisk, also injected once weekly. STEP trial data showed similar common side effects (nausea, diarrhoea, constipation) with dizziness occurring in some participants.
The key difference is mechanism: Mounjaro's dual action on both GIP and GLP-1 pathways may affect appetite regulation and gastric emptying slightly differently than Wegovy's single GLP-1 pathway. Neither mechanism directly causes dizziness, but indirect effects — such as reduced food intake, changes in blood glucose levels, or blood pressure fluctuations during dose titration — can contribute to lightheadedness in some users. Both are prescription-only medications requiring a UK prescriber's assessment before use. If you're experiencing dizziness, your prescriber may adjust your dose, review your hydration status, or investigate other underlying causes.
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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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When to Seek Help and Individual Suitability Factors
Dizziness that is severe, persistent, or worsening should be reported to your GP or prescriber immediately. Mild, occasional lightheadedness during the first few weeks of treatment or after a dose increase may settle as your body adjusts, particularly if you're staying well hydrated and eating regular, balanced meals. However, every person responds differently to these medications. Your prescriber will have assessed your personal health history — including blood pressure, blood sugar status, current medications, and other conditions — when determining which medication and dose is suitable for you.
Use our free BMI calculator and GLP-1 weight loss calculator to understand your baseline health metrics and projected outcomes with either medication. If dizziness persists, do not stop your medication without guidance from your prescriber. Instead, contact your GP or the healthcare provider who prescribed your treatment to discuss timing, dose adjustments, or whether an alternative medication might be more suitable for your individual circumstances.
- 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 or Wegovy?
Dizziness is not listed as a very common or common side effect in the clinical trials for either medication. However, some users report mild lightheadedness, particularly during dose titration or if dehydrated. Nausea, diarrhoea, and abdominal pain are more frequently reported. If you experience dizziness, inform your prescriber so they can assess the cause and determine whether it's related to the medication, dehydration, blood sugar changes, or other factors.
What causes dizziness with GLP-1 and GIP/GLP-1 medications like Mounjaro and Wegovy?
Dizziness is typically indirect rather than a direct effect of the medication's mechanism. Possible causes include reduced calorie intake leading to low blood sugar, dehydration, blood pressure drops, or changes in how quickly food leaves your stomach during dose titration. These effects usually improve with adequate hydration, regular meals, and time for your body to adjust. Your prescriber can help identify the specific cause in your case.
Should I stop taking Mounjaro or Wegovy if I feel dizzy?
Do not stop your medication without consulting your prescriber. Stopping abruptly can affect your weight management progress and may cause other issues. Instead, contact your GP or prescriber immediately to discuss your symptoms. They may recommend dose adjustments, hydration strategies, eating pattern changes, or further investigation to identify the cause and find a solution that works for you.
How do the side effect profiles of Mounjaro and Wegovy compare for dizziness?
Clinical trial data shows both medications have similar side effect rates overall, with nausea and gastrointestinal effects being most common. Dizziness is not prominently reported in either the SURMOUNT or STEP trials. However, individual responses vary significantly. Your prescriber's choice between them is based on your personal health profile, not on dizziness risk alone, as other factors like blood sugar control and comorbidities are more influential in determining suitability.
If I experience dizziness on one medication, will the other be safer?
Not necessarily. Both medications work through similar appetite-regulating pathways, so dizziness risk is comparable. If dizziness is related to dose, hydration, or food intake patterns, switching medications may not resolve it without addressing the underlying cause. Your prescriber may first try adjusting your current medication, hydration strategy, or meal patterns before considering a switch. Individual suitability is assessed case-by-case during clinical review.
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