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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Is Itching a Side Effect of Mounjaro?
Itching is not listed as a common or very common side effect of Mounjaro (tirzepatide) in the UK prescribing information. However, some people have reported skin itching during treatment. Itching can occasionally occur as part of injection site reactions or as an uncommon response to the medication. If you're experiencing itching whilst taking Mounjaro, it's important to understand whether it's directly related to the injection or a separate issue. This guide explains what we know about itching and Mounjaro in the UK NHS context, and when to contact your GP.
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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.
Understanding Mounjaro Side Effects and Skin Itching
Mounjaro is a prescription-only GIP and GLP-1 receptor agonist injection licensed in the UK for weight management in eligible adults. According to the MHRA-approved prescribing information, the most common side effects affect the digestive system — nausea, diarrhoea, vomiting, and constipation are experienced by more than 1 in 10 people.
Itching specifically is not listed among very common (>1 in 10) or common (1 in 10) side effects. However, skin reactions at the injection site — such as redness, bruising, and pain — are documented as common. Itching at the injection site occasionally occurs as part of these local reactions. Generalised itching (pruritus) across the body is extremely rare but has been reported in post-marketing surveillance. If you experience itching, it may be unrelated to Mounjaro entirely — allergies, dry skin, or other conditions can cause itching independently. Your GP can help determine the cause.
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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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What to Do If You're Experiencing Itching on Mounjaro
If you develop itching at your injection site, this is likely a minor local reaction. Rotate your injection sites weekly as recommended, apply a cool compress, and avoid scratching. Most injection site reactions settle within a few hours or days. If itching is severe, persistent, or spreading, contact your GP or call NHS 111 for advice.
If you experience itching across your body (generalised itching) whilst on Mounjaro, contact your GP. This could indicate an allergic reaction, though true allergies to tirzepatide are very rare. Your GP may adjust your dose, switch you to an alternative medication like Wegovy (semaglutide), or investigate other causes. Never stop Mounjaro suddenly without medical advice. Use our free BMI calculator to track your weight progress whilst managing any side effects with your healthcare team.
- 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 listed side effect of Mounjaro in the UK?
Itching is not listed as a very common or common side effect in the official MHRA prescribing information for Mounjaro. However, injection site itching can occur as part of local reactions, and generalised itching has been rarely reported. If you're experiencing itching, discuss it with your GP to establish the cause.
How common are injection site reactions with Mounjaro?
Injection site reactions (redness, bruising, pain) are common and affect up to 1 in 10 people taking Mounjaro. Most are mild and temporary. Rotating your injection site weekly and using a cool compress can help minimise these reactions.
Should I stop taking Mounjaro if I develop itching?
No — never stop Mounjaro without medical guidance. Contact your GP first to discuss the itching. Your prescriber can assess whether it's related to Mounjaro or another cause, and decide whether to continue, adjust your dose, or switch to an alternative medication.
Could itching be an allergic reaction to Mounjaro?
True allergic reactions to tirzepatide are extremely rare. If you develop sudden severe itching, swelling of the face, lips, or throat, or difficulty breathing, seek emergency medical help by calling 999. Most itching with Mounjaro is local or unrelated to the medication.
What's the difference between Mounjaro and Wegovy side effects?
Mounjaro (tirzepatide) and Wegovy (semaglutide) are both GLP-1 medications with similar common side effects — nausea, diarrhoea, constipation. Mounjaro is a dual GIP/GLP-1 agonist, whilst Wegovy is GLP-1 only. Both can cause injection site reactions. Your GP can help decide which is more suitable for you.
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