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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Can Mounjaro Cause Itchy Skin?
Itchy skin is not listed as a common or very common side effect of Mounjaro (tirzepatide) in UK clinical data and NHS guidance. However, some people do report skin-related changes when taking GLP-1 and GIP/GLP-1 medications. This guide explains what the evidence shows, when to seek advice from your GP, and how to manage skin changes while using Mounjaro as part of your weight management journey with NHS or private prescribing services.
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Enter your height and weight below. Supports both imperial (stone & lbs) and metric (kg). Results include NHS category, healthy weight range, and ethnicity adjustments.
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.
What Does the Evidence Show About Mounjaro and Skin Changes?
In the SURMOUNT clinical trials and NHS surveillance data, itching or pruritus is not recorded as a direct side effect of tirzepatide. The most common side effects reported are gastrointestinal — nausea, diarrhoea, vomiting, and constipation — which typically occur during dose escalation and improve over time.
However, skin-related changes can occur indirectly through several mechanisms: gradual weight management itself can cause skin irritation or dryness; dehydration from gastrointestinal side effects may lead to itchy or flaky skin; and injection site reactions (redness, bruising, localised irritation) are documented in clinical trials. Additionally, some people report hair loss (alopecia) on Mounjaro, which may be accompanied by scalp sensitivity.
- Documented injection site reactions: localised redness, bruising, or pain at the injection site — this is different from generalised itching
- Dehydration-related dryness: if nausea or diarrhoea causes fluid loss, dry skin can result
- gradual weight management effects: loose or stretching skin during significant weight loss may feel uncomfortable or itchy
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How It Works
Three simple steps to understand your weight and take action.
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.
Free Weight Loss Tools & Guides
Everything you need to understand your weight, explore medication options, and track your progress — completely free.
When Should You Contact Your GP About Skin Changes?
If you experience itching while taking Mounjaro, contact your GP or the healthcare professional managing your prescription if: the itching is severe or persistent; it appears as a rash or hives; it spreads across your body; or it is accompanied by other signs of an allergic reaction (facial swelling, difficulty breathing, throat tightness).
These symptoms may indicate an allergic reaction to tirzepatide or ingredients in the Mounjaro KwikPen, which would require stopping the medication immediately. Mild, temporary itching at the injection site alone is less concerning and often resolves within hours. Keep a brief record of when itching occurs and what you were doing — this helps your GP assess whether it is connected to the injection, diet, hydration, or an unrelated skin condition.
- 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 itchy skin a known side effect of Mounjaro in the UK?
Itching is not listed as a common or very common side effect of Mounjaro in NHS guidance or MHRA product information. However, indirect causes — such as dehydration from nausea or diarrhoea, gradual weight management, or injection site irritation — can occasionally trigger skin changes. Always consult your prescriber if you notice new or unusual symptoms.
Could Mounjaro cause an allergic reaction with itching and rash?
Yes. Although rare, allergic reactions to tirzepatide are possible. Signs include generalised itching, hives, facial swelling, or difficulty breathing. These are medical emergencies — stop the injection immediately and seek urgent medical help. Contact NHS 111 or A&E if symptoms are severe.
How can I manage dry skin while taking Mounjaro?
Stay well hydrated — dehydration from GI side effects can dry skin. Use gentle, fragrance-free moisturisers, avoid very hot showers, and wear breathable clothing. If nausea affects your fluid intake, try small sips of water or sugar-free drinks. Discuss persistent dryness with your GP.
Could hair loss and itchy scalp be related on Mounjaro?
Hair loss (alopecia) is documented with Mounjaro and may occur alongside scalp sensitivity. This is typically temporary and related to gradual weight management or metabolic changes. If scalp itching is severe, inform your healthcare provider — medicated shampoos may help manage symptoms.
What's the difference between injection site itching and generalised itching on Mounjaro?
Injection site reactions (local redness, bruising, mild discomfort) are common and usually harmless, resolving within hours. Generalised itching across your body is less typical and could signal an allergic reaction or other issue — contact your GP if it persists or spreads.
Ready to take control of your weight loss journey?
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