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
Does Mounjaro Make You Itch?
Itching is not listed as a common side effect of Mounjaro (tirzepatide) in clinical trials, though some people do report skin-related reactions. The most frequently reported side effects involve the digestive system — nausea, diarrhoea, and constipation — rather than itching. However, injection site reactions including redness and mild irritation can occasionally occur at the site where you inject the Mounjaro KwikPen. If you experience persistent itching during treatment, it's important to discuss this with your GP or the prescriber managing your weight loss journey.
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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.
Mounjaro Side Effects — What's Common and What's Not
Common Mounjaro side effects (affecting up to 1 in 10 people) include nausea, vomiting, diarrhoea, and constipation — these typically occur during dose titration as your body adjusts to each new dose level. Stomach pain, indigestion, and acid reflux are also relatively common. Itching is not officially listed as a common side effect in the product information, though some patients on online forums report mild skin irritation or itching sensations.
- Injection site reactions are more frequently reported than generalised itching — these appear as redness, bruising, or mild discomfort where you inject the Mounjaro KwikPen
- Any allergic reaction causing severe itching, swelling of the face or lips, or difficulty breathing requires immediate medical attention — contact NHS 111 or A&E
- Itching paired with rash or hives may indicate a skin allergy and should be assessed by your GP
Most side effects improve as your body adjusts to the medication during dose titration — typically within a few weeks at each new dose.
Clinically BackedWeight Loss
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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 Mounjaro Itching
If you experience itching while taking Mounjaro, contact your GP or the prescriber managing your treatment if the itching is:
- Persistent (lasting more than a few days)
- Severe or affecting your sleep or daily life
- Accompanied by a rash, hives, or blistering
- Part of a widespread allergic reaction (swelling, difficulty breathing, or throat tightness)
Do not stop taking Mounjaro without advice from your prescriber. Try to note when the itching occurs — for example, immediately after injection or several hours later — as this information helps your GP assess whether it's a true medication effect or injection site irritation. Our GLP-1 weight loss calculator can help you track how you're responding to your dose, including any side effects you experience.
- 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?
Itching is not listed as a common side effect of Mounjaro (tirzepatide) in clinical trials. However, some patients report mild skin irritation. The most common side effects involve the digestive system — nausea, diarrhoea, and constipation — rather than itching. Any unusual skin symptoms should be reported to your GP or prescriber.
What are the most common Mounjaro side effects in the UK?
The very common side effects (affecting more than 1 in 10 people) include nausea, diarrhoea, vomiting, and constipation. These typically occur during dose titration and often improve within a few weeks. Stomach pain, indigestion, and injection site redness are also frequently reported. Most side effects are mild to moderate.
Could itching be an allergic reaction to Mounjaro?
Itching could indicate an allergic reaction, especially if accompanied by rash, hives, swelling of the face or lips, or difficulty breathing. Serious allergic reactions to Mounjaro are rare but require immediate medical attention — contact NHS 111 or A&E. If you notice these symptoms, do not inject another dose and seek urgent medical assessment.
What should I do if I itch after injecting Mounjaro?
If itching occurs specifically at the injection site, it may be a localised reaction. Rotate your injection sites weekly using the abdomen, upper thigh, or upper arm. If itching is generalised (whole-body), contact your GP. Keep a note of when itching occurs relative to injection and any other symptoms — this helps your prescriber assess the cause.
Can Mounjaro cause skin conditions like eczema or psoriasis?
Mounjaro is not known to trigger or worsen eczema or psoriasis. However, if you have a history of these conditions and notice changes during treatment, inform your GP. Some people experience hair loss (alopecia) with Mounjaro, which is a listed side effect, but true skin conditions are not commonly associated with tirzepatide use.
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.