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
Free tracker included with every download this week
Mounjaro And Itchy Skin: What You Need To Know
Itchy skin is not listed as a common or very common side effect of Mounjaro (tirzepatide) in the UK prescribing information. However, some people using this GLP-1 and GIP receptor agonist injection have reported itching or skin irritation. This guide explains what the clinical evidence shows, when itching may be related to Mounjaro, and when to contact your GP. If you're considering weight loss medication, use our free GLP-1 weight loss calculator to explore potential outcomes with different doses.
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Calculate Your BMI Instantly
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.
Is Itchy Skin A Known Mounjaro Side Effect?
Itchy skin is not listed as a common or very common side effect in the MHRA-approved prescribing information for Mounjaro. The most frequently reported side effects during clinical trials were nausea, diarrhoea, vomiting, and constipation — all related to how tirzepatide affects the digestive system.
However, itching and skin reactions can occur with any medication, and some people using Mounjaro have reported pruritus (medical term for itching). This may occur for several reasons: as a rare individual sensitivity to tirzepatide, as part of an allergic reaction (which would require immediate medical attention), or as an unrelated coincidence.
The KwikPen injection itself can sometimes cause localised injection site reactions, including redness, bruising, or itching at the injection site — this is more common and usually mild and temporary. Rotating your injection site each week (stomach, thigh, or upper arm) can help minimise this.
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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 To Contact Your GP About Itching
Contact your GP or prescriber if itching is:
- Severe or spreading — could indicate an allergic reaction
- Accompanied by swelling of the face, lips, tongue, or throat — seek urgent medical attention immediately
- Persistent and affecting your daily life — your GP can assess whether it's related to Mounjaro or another cause
- Getting worse over time — may need dose adjustment or medication review
Mild itching at the injection site that resolves within a few hours is usually not a cause for concern. If you're tracking your Mounjaro progress and side effects, our free progress tracker can help you log symptoms and share them with your prescriber.
- 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 common side effect of Mounjaro?
No. Itchy skin is not listed as a common or very common side effect in UK prescribing information for Mounjaro (tirzepatide). The most common side effects are nausea, diarrhoea, vomiting, and constipation. However, itching has been reported rarely and may occur as an individual reaction.
Could itching be an allergic reaction to Mounjaro?
Possibly, but rarely. If itching is accompanied by swelling of the face, lips, tongue, or throat, or difficulty breathing, seek urgent medical attention as this could indicate a serious allergic reaction. Mild localised itching is usually not an allergic reaction.
Why might I get itchy skin at the injection site?
Injection site reactions, including itching, redness, and bruising, are more common than itching from the medication itself. Rotating your injection site each week between the stomach, thigh, and upper arm can help reduce these reactions.
What should I do if Mounjaro is making my skin itchy?
Contact your prescriber or GP. If itching is mild and only at the injection site, it may resolve on its own. If it's severe, spreading, or persistent, your GP can assess whether it's related to Mounjaro or another cause and discuss next steps, which may include dose adjustment.
How does Mounjaro's mechanism differ from other weight loss injections like Wegovy?
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, whilst Wegovy (semaglutide) is a GLP-1 agonist only. Both work on appetite and digestion but through slightly different pathways. Side effect profiles are similar overall, though individual responses vary. Your prescriber can advise which is more suitable for you.
Ready to take control of your weight loss journey?
Start with a free BMI check, explore your GLP-1 options, or begin tracking your progress today. No sign-up. No cost. Just results.