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 — Comparison with Wegovy
Hair loss (alopecia) is a documented side effect reported by some people taking Mounjaro and Wegovy. It's typically temporary and related to gradual weight management rather than the medication itself, but understanding the differences between these weekly weight loss injections and how to manage hair loss is important if you're considering either treatment. This guide compares the two medications, explains why it happens, and suggests what you can do about it. Always discuss any concerns with your GP before starting treatment.
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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.
Mounjaro vs Wegovy — Hair Loss in Clinical Trials
Hair loss occurs in both Mounjaro and Wegovy but is not among the most commonly reported side effects in clinical trials. In the SURMOUNT-1 trial for Mounjaro (tirzepatide), hair loss (alopecia) was reported by some participants but occurred in a small percentage. Similarly, in the STEP trials for Wegovy (semaglutide), hair loss was documented but not classified as a "very common" or "common" side effect.
The key difference is the mechanism: Mounjaro is a dual GIP and GLP-1 receptor agonist, whereas Wegovy is a GLP-1 receptor agonist only. This dual action may influence weight loss rate and how the body responds, though both can cause gradual weight management, which is the primary driver of telogen effluvium (temporary shedding). Hair loss with these medications is usually reversible and typically resolves within months after stopping treatment or stabilising at a maintenance dose.
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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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Managing Hair Loss — Practical Steps
If you experience hair loss while taking Mounjaro or Wegovy, several strategies may help. Ensure you're eating adequate protein (1.2–1.6g per kg of body weight daily) to support hair growth, as gradual weight management can deplete nutrient stores. Take a multivitamin with zinc, iron, and B vitamins — deficiencies are linked to hair shedding. Stay hydrated and prioritise whole foods over ultra-processed options.
Inform your GP or prescriber if hair loss is significant or distressing. They may suggest slowing your dose escalation, which can reduce the rate of weight loss and potentially minimise shedding. Hair loss usually stops once your weight stabilises. Consider using the GLP-1 weight loss calculator on this page to understand your projected weight loss timeline — slower, sustained loss is often gentler on your body than rapid loss.
- 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 with Mounjaro or Wegovy?
No. Hair loss with these medications is typically temporary and related to gradual weight management (telogen effluvium), not the drug itself. It usually reverses within 3–6 months after stopping the injection or once your weight stabilises at a maintenance dose. If it persists beyond this, consult your GP as other causes may be involved.
How does Mounjaro's dual mechanism affect hair loss compared to Wegovy?
Mounjaro (tirzepatide, dual GIP/GLP-1) and Wegovy (semaglutide, GLP-1 only) both cause weight loss, which is the main trigger for telogen effluvium. Clinical trial data doesn't show significantly higher hair loss rates with Mounjaro versus Wegovy, though individual responses vary. Your prescriber can help you choose based on your overall health profile.
Can I prevent hair loss if I take Mounjaro or Wegovy?
You can minimise it by ensuring adequate protein intake, taking vitamins (especially iron, zinc, B vitamins), staying hydrated, and eating nutrient-dense foods. Slowing your dose titration through gradual escalation also helps — a slower weight loss rate is gentler on your body. Discuss this with your GP or prescriber before starting.
What should I do if I'm experiencing significant hair loss on these injections?
Report it to your GP or prescriber. They can review your dose, adjust your escalation schedule, or discuss whether continuing is right for you. Ensure you're also addressing nutritional factors. Hair loss usually improves once weight loss slows or stabilises, but professional guidance is important.
Which medication — Mounjaro or Wegovy — causes less hair loss?
Clinical evidence doesn't show a clear superiority of one over the other regarding hair loss. Both are associated with it as a rare to uncommon side effect, primarily driven by gradual weight management rather than the drug mechanism. Your GP will recommend whichever is more suitable for your individual health needs.
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