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 Hair Loss Side Effects vs Wegovy
Hair loss (alopecia) has been reported by some people using both Mounjaro and Wegovy, the two most commonly prescribed weekly weight loss injections in the UK. This page compares the reported frequency, clinical trial evidence, and mechanisms behind hair loss with these prescription weight loss medications. Understanding the differences can help you and your GP or prescriber make an informed decision about which treatment might suit you best.
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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 in Clinical Trials: Mounjaro vs Wegovy
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist approved for weight management as a weekly weight loss injection in the UK. In the SURMOUNT clinical trials, alopecia (hair loss) was reported as a common side effect, occurring in up to 1 in 10 people at higher doses (15 mg). Hair loss typically appeared during the early weeks of treatment and often improved over time as the body adjusted.
Wegovy (semaglutide) is a GLP-1 receptor agonist only, working through a single hormone pathway. In the STEP clinical trials, hair loss was also documented as a common side effect, but reported slightly less frequently than with Mounjaro. The mechanism differs because Wegovy only activates GLP-1 receptors, whereas Mounjaro's dual GIP+GLP-1 action may influence hair growth differently.
- Mounjaro: hair loss reported in clinical trials at common frequency
- Wegovy: hair loss reported at similar or slightly lower rates
- Both: individual experiences vary significantly
- Both: hair loss is not permanent and often improves
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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.
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Why Hair Loss Occurs and What Prescribers Consider
Hair loss with weight loss injections is thought to occur due to gradual weight management triggering a condition called telogen effluvium, where hair follicles shift prematurely into a resting phase. This is not unique to Mounjaro or Wegovy — it can happen with any significant weight loss. The stress on the body during calorie deficit may also play a role. Your prescriber will assess your individual risk factors, including family history of hair loss, during your clinical assessment for a UK prescription weight loss injection.
If hair loss is a significant concern, discuss this openly with your prescriber before starting treatment. They may suggest strategies to support hair and scalp health, such as adequate protein intake, micronutrient supplementation, and stress management. Hair loss is typically temporary, but understanding your personal risk helps you make an informed choice.
- 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 common with Mounjaro?
Hair loss (alopecia) was reported as a common side effect in SURMOUNT clinical trials, affecting up to 1 in 10 people. However, this varies significantly between individuals. Hair loss typically appears during early weeks and often improves as treatment continues. Discuss your personal risk factors with your prescriber before starting.
Does Wegovy cause less hair loss than Mounjaro?
Clinical trial data suggests Wegovy may have slightly lower reported rates of hair loss compared to Mounjaro, but the difference is not substantial. Both medications can trigger hair loss related to gradual weight management itself, not the medication alone. Individual experiences vary considerably regardless of which injection is prescribed.
Is the hair loss from these injections permanent?
No. Hair loss from weight loss injections is typically temporary and related to telogen effluvium — a condition caused by gradual weight management and body stress. Hair usually grows back once the body stabilises and weight loss slows. This is not permanent damage to hair follicles.
How can I reduce the risk of hair loss with weight loss injections?
Ensure adequate protein intake (aim for 1.2–1.6g per kg body weight), maintain good micronutrient levels (iron, zinc, biotin), manage stress, and stay hydrated. Some people find hair and scalp supplements helpful. Discuss these strategies with your GP or prescriber before starting Mounjaro or Wegovy.
Which injection should I choose if I'm concerned about hair loss?
Both Mounjaro and Wegovy carry hair loss risk. The choice depends on multiple factors assessed during your clinical evaluation — including your BMI, health conditions, and medical history. Your prescriber will help determine which prescription weight loss medication is most suitable for your individual circumstances, not hair loss risk alone.
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