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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Hair Loss with Mounjaro vs Wegovy — What the Evidence Shows
Hair loss (alopecia) is listed as a common side effect of Mounjaro in clinical trials, though it affects relatively few users. Wegovy also carries a small hair loss risk, but the two medications have different mechanisms and trial safety profiles. This guide compares the evidence, helps you understand the context, and explains how your prescriber decides between them based on individual health needs.
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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.
Clinical Trial Data and Mechanism Differences
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, meaning it activates two natural hormone pathways. In the SURMOUNT-1 clinical trial, hair loss was reported as a common side effect (affecting up to 1 in 10 people), though most cases were mild and reversible.
Wegovy (semaglutide) is a single GLP-1 receptor agonist. In the STEP clinical trials, hair loss was also reported but appears less frequently mentioned in trial summaries compared to Mounjaro. This may reflect the different patient populations studied, weight loss intensity, or reporting differences rather than true mechanistic superiority of one drug.
- Both medications cause gradual weight management, which itself can trigger temporary hair shedding (telogen effluvium) due to nutritional stress
- The dual mechanism of Mounjaro may affect metabolic processes differently than single GLP-1 action
- Individual variation is substantial — some users experience no hair loss, whilst others notice thinning within weeks
- Hair loss reported in trials is typically mild and often reverses after stopping treatment or completing dose stabilisation
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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.
Choosing Between Them — What Your Prescriber Considers
Your prescriber will not choose between Mounjaro and Wegovy based on hair loss risk alone. Instead, they assess your full health picture: existing health conditions, other medications, weight loss goals, BMI category, and personal preferences. Both are prescription-only medicines requiring a clinical assessment via a UK-licensed healthcare professional.
If you have a personal or family history of hair loss, mention this during your consultation. Your prescriber may choose Wegovy as a first option, monitor hair health more closely, or ensure you're meeting nutritional needs (adequate protein, iron, zinc) during gradual weight management. Try our free GLP-1 weight loss calculator to estimate potential weight loss projections at different doses — this can help inform your discussion with your prescriber about which medication might suit your goals.
- 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 hair loss permanent if I take Mounjaro?
No. Hair loss associated with Mounjaro is typically temporary and reverses after stopping the medication or once your body adjusts to the dose. Most cases are mild shedding rather than visible baldness. If you're concerned, speak to your GP — nutritional support and monitoring can help minimise shedding during treatment.
Does Wegovy cause less hair loss than Mounjaro?
Clinical trial data suggests hair loss reports are slightly less common with Wegovy, but differences may reflect trial population variation rather than true safety difference. Both medications can trigger hair shedding due to gradual weight management and metabolic changes. Individual experience varies widely — some users of either drug notice no hair changes at all.
Can I reduce hair loss risk when taking weight loss injections?
Yes. Ensure adequate protein intake, maintain iron and zinc levels, stay hydrated, and manage stress — all support hair health during gradual weight management. Speak to your GP or a registered dietitian about supplementation if needed. Slow, gradual dose increases (as designed in the titration schedule) may also help your body adapt better.
Should hair loss risk influence my choice between Mounjaro and Wegovy?
It's one factor among many, but not the primary decision-maker. Your GP will consider your BMI, health conditions, other medications, and weight loss goals. If hair loss is a significant concern for you personally, mention it during your consultation — your prescriber can discuss monitoring strategies and may adjust nutrition or follow-up care accordingly.
How quickly does hair loss happen with these injections?
Hair shedding typically begins 2–3 months after starting, peaks around 3–5 months, and often improves thereafter. This timeline reflects the normal hair growth cycle (telogen effluvium) triggered by gradual weight management, not a direct drug reaction. Most users notice improvement once weight loss stabilises or after treatment ends.
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.