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 Bruising On Legs?
Bruising on the legs is not a commonly reported side effect of Mounjaro (tirzepatide), though injection site reactions can occur where you administer the weekly dose. Most bruising associated with Mounjaro injections happens at the injection site itself — typically the stomach, thigh, or upper arm. If you're experiencing unexplained bruising on your legs away from injection sites, it's important to contact your GP to rule out other causes. This guide explains what's normal with Mounjaro, what side effects to expect, and when to seek medical advice.
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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.
Where Does Bruising Occur With Mounjaro?
Injection site bruising is the most common type of bruising related to Mounjaro. The KwikPen delivers a once-weekly injection into the stomach (abdomen), upper thigh, or upper arm. Minor bruising, redness, or swelling at the injection site is normal and typically resolves within a few days.
- Rotate injection sites each week to minimise bruising
- Allow skin to warm to room temperature before injecting
- Avoid injecting into areas with existing bruises or scars
- Ice the area for 10 minutes before injection if you bruise easily
Most tirzepatide users experience mild injection site reactions that don't require medical attention. However, bruising on your legs away from injection sites is unusual and warrants a conversation with your GP, as it could indicate a separate health concern unrelated to Mounjaro itself.
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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 Bruising
Contact your GP if you experience:
- Severe or spreading bruising away from injection sites
- Bruising accompanied by bleeding or blood in urine or stool
- Unexplained bruising that appears without injury
- Signs of infection at the injection site (increasing redness, warmth, pus)
- Bruising that worsens rather than improves after a few days
Your GP can assess whether the bruising is related to Mounjaro, a medication interaction, or another underlying condition. Always report new or concerning symptoms when taking any prescription medication, including tirzepatide. If you're unsure whether your symptoms warrant medical attention, call NHS 111 for guidance.
- 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 bruising a common side effect of Mounjaro?
Bruising at the injection site is a known but mild side effect, affecting around 1 in 100 users. Bruising elsewhere on the body is not a typical Mounjaro effect. Minor injection site bruising usually fades within days and doesn't require treatment. Report persistent or severe bruising to your GP.
Can Mounjaro interact with other medications to cause bruising?
Mounjaro can affect how oral medications are absorbed due to slowing gastric emptying. If you take blood thinners or medications affecting clotting, inform your prescriber before starting tirzepatide. Your GP or pharmacist can check for interactions and advise on timing doses.
How can I prevent bruising when using the Mounjaro KwikPen?
Rotate injection sites weekly between stomach, thigh, and upper arm. Avoid injecting into bruised areas. Allow the KwikPen to reach room temperature before use. Ice the injection site for 10 minutes beforehand if you're prone to bruising. Use a fresh needle for each injection and ensure proper injection technique.
Is there a difference between Mounjaro and Wegovy regarding bruising risk?
Both Mounjaro and Wegovy are once-weekly injections with similar injection site reaction profiles. Mounjaro is a dual GIP/GLP-1 agonist, whilst Wegovy is a GLP-1 agonist only. Clinical data shows no significant difference in bruising frequency between the two medications.
What other injection site side effects should I expect with Mounjaro?
Common injection site reactions include redness, swelling, and mild pain. These are normal and temporary. Serious reactions are rare but include signs of infection. Most users tolerate injections well. Report any concerning injection site changes to your GP or prescriber promptly.
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