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 and Skin Changes — What UK Patients Should Know
Mounjaro (tirzepatide) is a prescription-only weight management injection available in the UK through NHS specialist services and private prescribing. Some patients report skin-related changes including hair loss (alopecia) and dry skin during treatment. This guide explains what these changes are, whether they're common, and how to manage them within an NHS or private context. If you're considering Mounjaro or taking it, understanding potential skin effects helps 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.
Mounjaro and Skin Changes — What the Evidence Shows
Hair loss is listed as a common side effect of Mounjaro in UK clinical data, affecting approximately 1 in 10 patients during treatment. This typically appears as increased shedding rather than complete baldness. Dry skin and mild rashes at injection sites are also reported by some users. These changes are usually temporary and may improve once your body adjusts to the medication or after stopping treatment.
The KwikPen injection itself can cause localised skin reactions at the injection site — redness, bruising, or itching — which are listed as common side effects. Rotating injection sites each week (stomach, upper thigh, or upper arm) helps minimise these reactions. Most injection site reactions resolve within a few hours to days.
Important context: Hair loss during gradual weight management can occur independently of Mounjaro due to stress on the body. If you're losing weight quickly, your hair follicles may naturally shed more. This is separate from any medication effect. Your GP can help distinguish between medication-related and weight-loss-related hair shedding.
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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 Skin Changes — NHS and Private Guidance
If you experience skin changes while taking Mounjaro, document what you're seeing (when it started, severity, affected areas) and discuss it at your next appointment with your prescriber or GP. Most skin changes are mild and temporary, but your healthcare provider may adjust your dose or suggest skincare measures.
To support skin health during Mounjaro treatment: use gentle, fragrance-free skincare products; stay hydrated; ensure adequate protein intake (important during weight loss to support hair and skin); and consider a scalp treatment or hair supplement if hair loss concerns you. Rotate injection sites consistently to avoid repeated skin irritation in the same area. If skin changes are severe or you develop signs of allergic reaction (swelling, severe rash), seek medical advice promptly.
- 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 from Mounjaro permanent?
No. Hair loss with Mounjaro is typically temporary. It usually resolves after stopping treatment or as your body adjusts. Hair shedding during gradual weight management can naturally slow once weight loss stabilises. If shedding persists months after stopping, discuss with your GP — other causes may be involved.
How common is skin irritation at the injection site?
Injection site reactions (redness, bruising, mild itching) are common, affecting up to 1 in 10 patients. Most resolve within hours or days. Rotating your injection site weekly between stomach, thigh, and upper arm minimises irritation. Always use a new needle and let the pen reach room temperature before injection.
Can I prevent hair loss while taking Mounjaro?
You cannot prevent medication-related hair loss entirely, but you can support overall health: eat adequate protein, stay hydrated, take a biotin or hair supplement if your GP approves, and manage stress. Much hair shedding during weight loss is temporary and related to rapid body change, not the medication alone.
Should I tell my GP about skin changes when on Mounjaro?
Yes. Always report any skin changes to your prescriber or GP, especially if they're severe, spreading, or causing distress. Most skin effects are mild, but your healthcare provider needs to know and can advise on management or whether your dose needs adjusting.
Are skin changes more common at higher Mounjaro doses?
No clear dose-dependent pattern for skin changes has been established in clinical data. Hair loss and skin reactions can occur at any dose. If skin changes worsen when you increase your dose, discuss this with your prescriber — they can assess whether continuing at that dose is right for you.
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