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 Hairloss vs Wegovy — What's the Difference?
Hair loss (alopecia) is a reported side effect of both Mounjaro and Wegovy weight loss medications. Both are prescription-only GLP-1-based treatments used in the UK for weight management, but they work differently and may affect individuals differently. This guide compares hairloss reports between Mounjaro (tirzepatide, the dual GIP+GLP-1 agonist) and Wegovy (semaglutide, a GLP-1-only agonist) based on clinical trial data and UK prescribing information, helping you understand what the evidence actually shows.
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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 — Hairloss Reporting Rates
Mounjaro (tirzepatide): Hair loss was reported as a common side effect in SURMOUNT clinical trials, affecting approximately 1 in 10 people at the maximum 15 mg dose. In the SURMOUNT-1 trial, hairloss rates increased slightly at higher doses, though it remained manageable for most participants.
Wegovy (semaglutide): Hair loss was also reported during STEP trials, though at slightly lower frequencies in some cohorts. It appears in the "common" side effects list, meaning it may affect up to 1 in 10 people. Reports suggest hairloss is often temporary and may stabilise as the body adjusts to the medication.
- Both medications can trigger telogen effluvium (temporary shedding due to stress on hair follicles)
- gradual weight management itself can contribute to temporary hair loss, independent of the medication
- Individual responses vary significantly — some people experience no hairloss at all
- Your GP or prescriber can discuss personal risk factors before starting either medication
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Key Mechanism Differences and Hairloss Context
Mounjaro uses a dual GIP+GLP-1 mechanism, activating two hormone pathways simultaneously. This dual approach may produce slightly different side effect profiles compared to Wegovy's single GLP-1 mechanism. However, hairloss appears in clinical data for both, suggesting it may be linked more to gradual weight management itself than to the specific medication type.
Hairloss is often temporary during weight loss treatment — hair typically regrows once weight stabilises and stress on the body reduces. If you're concerned about hairloss before starting either medication, discuss this with your GP. Your prescriber can assess whether either Mounjaro or Wegovy is suitable for you based on your individual health profile, and advise on managing side effects. Use our free BMI calculator above to check your current weight status, and our GLP-1 weight loss calculator to explore how either medication might affect your weight loss timeline.
- 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.
Which causes more hairloss — Mounjaro or Wegovy?
Clinical trial data suggests hairloss rates are similar between both medications, occurring in roughly 1 in 10 people. Mounjaro (tirzepatide) reported hairloss at comparable frequencies to Wegovy (semaglutide) in their respective trials. Individual responses vary — some people experience no hairloss at all. Your prescriber can discuss personal risk factors.
Is hairloss from Mounjaro or Wegovy permanent?
Hairloss during weight loss treatment is typically temporary, often caused by the stress of gradual weight management on hair follicles (telogen effluvium). Hair usually regrows once weight stabilises. Permanent hairloss is rare. If hairloss persists beyond treatment, consult your GP.
Can I reduce hairloss risk while taking Mounjaro or Wegovy?
You cannot eliminate the risk, but you can support hair health: maintain adequate protein intake, manage stress, ensure sufficient sleep, and consider a biotin-rich diet. Slower weight loss (0.5–1 kg per week) may also reduce hairloss risk. Discuss nutritional support with your GP or a registered dietitian.
Does hairloss start immediately or later during treatment?
Hairloss typically emerges after 2–4 weeks of treatment as the body responds to medication and weight loss begins. It is not usually immediate. Most people who experience hairloss notice it during the first 8–12 weeks, then it typically stabilises or improves.
Should I avoid Mounjaro or Wegovy if I'm worried about hairloss?
Hairloss is one possible side effect, but it affects only about 1 in 10 people and is usually temporary. Many people tolerate both medications without hairloss. Your prescriber can assess your individual risk and discuss whether the health benefits outweigh the side effect risk for you.
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