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
Why Does My Mounjaro Injection Site Itch?
An itchy injection site is a common reaction to Mounjaro (tirzepatide), the prescription-only weight loss injection used by adults across the UK. Itching at the injection site typically occurs as a mild, temporary response to the injection itself and usually resolves within a few hours to a few days. While it can be uncomfortable, it's generally not serious — but knowing when to be concerned and how to manage it safely is important.
10,000+ calculations today · NHS-aligned thresholds · 100% free
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.
Understanding Injection Site Reactions
Mounjaro is a once-weekly GIP and GLP-1 receptor agonist injection, delivered via a pre-filled KwikPen device. Common injection site reactions include redness, bruising, swelling, and itching. The itching typically occurs because:
- The needle punctures the skin, triggering a mild inflammatory response
- The medication itself may cause localised irritation as it's absorbed
- Skin sensitivity varies between individuals — some people experience more noticeable reactions than others
- Rotating injection sites (stomach, thigh, upper arm) can reduce irritation if you're reusing similar areas
According to clinical trial data, injection site reactions are common but usually mild. Most people find that reactions improve as their body adjusts to the injections over the first few weeks. If you're using a weekly weight loss injection for the first time, some initial discomfort is normal.
Clinically BackedWeight Loss
No appointments. No waiting rooms. Just care — from a UK-regulated online pharmacy.
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 Seek Medical Advice
While mild itching is normal, you should contact your GP or prescriber if you experience:
- Severe itching that doesn't improve after a few days
- Signs of infection (increasing warmth, pus, spreading redness)
- Severe allergic reaction (swelling of lips, tongue, or throat)
- Itching accompanied by blistering or open sores
- Itching that worsens with each injection despite rotating sites
Most people tolerate Mounjaro well, and injection site reactions tend to decrease over time as your body adjusts. If you're concerned about your specific symptoms, your GP or the prescriber who issued your UK prescription can provide personalised guidance based on your health.
- 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 at the Mounjaro injection site normal?
Yes, mild itching is a common and usually temporary injection site reaction. It typically resolves within a few hours to several days and is generally not a sign of a serious problem. However, if itching is severe or persistent, contact your GP.
How can I reduce itching at my Mounjaro injection site?
Rotate your injection sites weekly between stomach, upper thigh, and upper arm to avoid repeated irritation to the same area. Avoid scratching the site, keep it clean and dry, and consider applying a cold compress for temporary relief if needed.
Should I stop taking Mounjaro if my injection site itches?
No — mild itching alone is not a reason to stop treatment. Continue your weekly dose as prescribed. However, if you have concerns about the severity of your reaction, contact your prescriber before your next injection.
What's the difference between normal itching and a sign of infection?
Normal itching is localised and temporary. Signs of infection include spreading redness, warmth, pus, or worsening symptoms over several days. If you notice these signs, contact your GP or prescriber promptly.
Can I use a cream or lotion on an itchy Mounjaro injection site?
For simple itching, a plain moisturiser is generally safe. Avoid scratching and keep the area clean. If you want to use a medicated cream, check with your GP first to ensure it won't interfere with your treatment. Avoid thick occlusive dressings.
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.