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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Does Mounjaro Cause Hair Loss?
Hair loss is a recognised side effect of Mounjaro, reported in clinical trials and by users in the UK. However, it's relatively uncommon — classified as a "common" side effect affecting up to 1 in 10 people. Both Mounjaro and Wegovy, the two most widely used weekly weight loss injections in the UK, can potentially cause hair loss, though rates and severity vary between individuals. Understanding the differences between these prescription weight loss medications can help you make an informed decision with your GP or prescriber.
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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.
Hair Loss with Mounjaro vs Wegovy — Clinical Evidence
In the SURMOUNT-1 clinical trial, hair loss (alopecia) was reported in approximately 6% of people taking Mounjaro, making it a common but not extremely frequent side effect. This compares with Wegovy, where hair loss occurred in a smaller percentage of participants during the STEP trials — though exact figures vary by study.
Hair loss associated with weight loss injections typically occurs because:
- gradual weight management can temporarily disrupt hair growth cycles, pushing more hairs into a shedding phase (telogen effluvium)
- The stress of significant dietary changes and metabolic shifts may affect hair follicles
- Nutritional shifts during weight loss can impact hair health if protein or micronutrient intake is inadequate
Both Mounjaro (tirzepatide, a dual GIP and GLP-1 receptor agonist) and Wegovy (semaglutide, a GLP-1-only medication) work through similar appetite-regulating mechanisms, which may explain why both can trigger this side effect. Hair loss with these medications is usually temporary and resolves after stopping treatment or as the body adjusts — though individual experiences vary significantly.
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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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Managing Hair Loss — Individual Suitability Assessment
Whether you experience hair loss on Mounjaro, Wegovy, or neither is highly individual and difficult to predict. Your prescriber will assess your personal medical history, current medications, and nutritional status before recommending a weekly weight loss injection. If you have a history of hair loss conditions (such as alopecia or telogen effluvium), inform your prescriber — they may suggest additional nutritional support or consider an alternative approach.
If hair loss does occur during treatment, most cases resolve within weeks to months after stopping the medication or as your body adjusts to a slower dose escalation. Maintaining adequate protein intake, managing micronutrient levels, and following a balanced reduced-calorie diet — rather than severely restrictive eating — can support hair health during weight loss. Only a licensed prescriber can assess whether Mounjaro, Wegovy, or another treatment is appropriate 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.
Does Mounjaro cause more hair loss than Wegovy?
Hair loss rates differ slightly between trials. Mounjaro showed approximately 6% in SURMOUNT-1; Wegovy showed lower rates in STEP trials. However, individual experiences vary greatly — some people experience no hair loss on either medication. Your prescriber can discuss individual risk factors with you.
Is hair loss from Mounjaro permanent?
No. Hair loss associated with weight loss injections is typically temporary and classified as telogen effluvium — a temporary shedding phase. Hair usually regrows weeks to months after stopping treatment or as your body adjusts. Permanent hair loss is rare.
Can I prevent hair loss while taking Mounjaro?
Ensure adequate protein intake, maintain micronutrient levels (iron, zinc, B vitamins), avoid very restrictive dieting, and follow a balanced reduced-calorie diet. Slower dose titration may also help. Discuss any concerns with your prescriber or a registered dietitian.
Should I avoid Mounjaro if I'm worried about hair loss?
Not necessarily. Most people taking Mounjaro don't experience hair loss. Your prescriber will assess your individual risk factors and medical history. If you have a history of hair loss conditions, mention this during your clinical assessment — they can advise accordingly.
Is hair loss listed as a side effect on the Mounjaro information?
Yes. Hair loss (alopecia) is listed as a "common" side effect in the UK Mounjaro patient information leaflet, meaning it may affect up to 1 in 10 people. Always read the full information leaflet provided with your medication and discuss any concerns with your healthcare provider.
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