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
Can Mounjaro Cause Itching?
Itching is not listed as a common side effect of Mounjaro (tirzepatide) in UK prescribing information, but skin reactions including itching can occasionally occur. If you experience persistent itching after starting your Mounjaro injection, it's important to understand whether it's related to the medication or another cause. This guide explains what the NHS advises about Mounjaro side effects and when to contact your GP for reassurance or alternative options.
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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.
What Does the MHRA Say About Mounjaro Skin Side Effects?
Itching is not a "common" or "very common" side effect of Mounjaro according to MHRA prescribing data. However, injection site reactions—including redness, bruising, and pain at the injection site—are reported. In rare cases, people have reported generalised skin itching or pruritus, which may be linked to allergic sensitivity to the medication or its ingredients.
- Injection site reactions (redness, bruising, irritation) are the most common skin-related side effects
- Allergic reactions are rare but can cause itching, rash, or swelling
- Itching may also be unrelated to Mounjaro—stress, dry skin, or other medications can trigger it
- Your GP can review whether itching is medication-related using your medical history
If you develop itching shortly after starting a new Mounjaro dose, mention it to your prescriber at your next check-in. Persistent or severe itching warrants prompt contact with your GP.
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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.
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When to Contact Your GP About Itching on Mounjaro
Contact your GP or prescriber if itching is severe, persistent, spreading, or accompanied by other symptoms such as rash, swelling, difficulty breathing, or hives. These could indicate an allergic reaction requiring urgent assessment. If itching is mild and localised to the injection site, it may settle within a few days as your skin adapts. Keep a brief record of when itching occurs and any other symptoms—this helps your GP determine if it's Mounjaro-related or another cause. Your prescriber may adjust your dose, switch injection sites, or recommend a different medication if itching significantly affects your quality of life.
- 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 itching a known side effect of Mounjaro in the UK?
Itching is not listed as a common side effect by the MHRA. Injection site reactions (redness, bruising) are more typical. Generalised itching is rare but has been reported in some users. If you experience itching, your GP can assess whether it's related to Mounjaro or another cause.
What should I do if I develop itching after my Mounjaro injection?
Monitor the itching for a few days—mild, localised itching at the injection site often settles naturally. If itching is severe, spreading, persistent, or accompanied by rash or swelling, contact your GP or prescriber promptly. Keep notes on when it occurs and any other symptoms to share with your doctor.
Could itching be an allergic reaction to Mounjaro?
Allergic reactions to Mounjaro are rare but possible. Signs include itching with rash, swelling (face, lips, throat), or difficulty breathing. These require urgent medical attention. Mild, localised itching alone is unlikely to be a serious allergic reaction, but your GP can clarify this during a consultation.
Should I stop taking Mounjaro if I develop itching?
Do not stop Mounjaro without speaking to your prescriber first. If itching is mild and manageable, continuing may be appropriate. If it's severe or affecting your wellbeing, your GP can assess whether to adjust your dose, change injection sites, or consider an alternative weight management option.
Can I use our free GLP-1 weight loss calculator while managing Mounjaro side effects?
Yes. Our GLP-1 calculator helps you track projected weight loss across different doses, which is useful if your prescriber suggests adjusting your Mounjaro dose due to side effects like itching. Having clear weight loss expectations can support informed decisions with your GP about next steps.
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.