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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Can Mounjaro Cause Bruising on Legs?
Bruising can occasionally occur with Mounjaro (tirzepatide) injections, though it's not a common side effect. Mounjaro is a once-weekly GLP-1 and GIP receptor agonist medication that requires a UK prescription. Most bruising from injections is mild and temporary, appearing at injection sites rather than on the legs themselves. If you're considering Mounjaro or comparing it with Wegovy, understanding potential injection-related side effects can help you decide which prescription weight loss medication might suit you. Always discuss any concerns about bruising or other side effects with your GP or prescriber before starting treatment.
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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.
Mounjaro Bruising vs Wegovy — Clinical Context
Both Mounjaro (tirzepatide) and Wegovy (semaglutide) are prescription-only weight loss injections administered weekly. Bruising can occur with either medication, but it's classified as a common injection site reaction rather than a systemic side effect affecting the legs directly. In the SURMOUNT-1 clinical trial for Mounjaro, injection site reactions (including bruising, redness, and pain) were reported in up to 1 in 10 patients. The STEP-1 trial for Wegovy similarly reported injection site reactions as common side effects. The KwikPen delivery system used for Mounjaro may cause slight bruising if the needle pierces a small blood vessel, though this is typically minor. Wegovy's auto-injection pen carries similar bruising risk. Most injection-related bruising resolves within 1–2 weeks without treatment. Both medications require a clinical assessment before prescription, and your prescriber can advise on minimising injection-related reactions.
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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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Which Medication Causes More Bruising?
Evidence suggests both Mounjaro and Wegovy cause similar rates of injection site bruising — neither medication is notably more likely to cause bruising than the other. The difference lies in dose titration schedules: Mounjaro starts at 2.5 mg and escalates over weeks, while Wegovy begins at 0.25 mg. More frequent dose adjustments theoretically increase injection frequency, which may increase bruising likelihood. However, individual factors matter more than the medication type: injection technique, needle angle, anticoagulant use, and personal blood vessel fragility all influence bruising risk. Using the Mounjaro KwikPen correctly (holding skin folds, rotating injection sites, and using room-temperature pens) reduces bruising. If you develop persistent or painful bruising on your legs unrelated to injection sites, inform your GP immediately. Most bruising is minor and does not require stopping treatment — your prescriber can offer practical tips to minimise it.
- 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 on the legs a common side effect of Mounjaro?
Bruising at injection sites is common (up to 1 in 10 users), but bruising on the legs away from injection areas is rare. Most injection-related bruising is mild, temporary, and resolves within 1–2 weeks. If you develop unexplained leg bruising unrelated to injections, contact your GP.
Does Wegovy cause less bruising than Mounjaro?
Both medications cause similar rates of injection site bruising. Wegovy and Mounjaro carry comparable bruising risk. Individual factors like injection technique, skin sensitivity, and blood vessel fragility matter more than which medication you use.
How can I reduce bruising from Mounjaro injections?
Rotate injection sites weekly between stomach, thigh, and upper arm. Pinch skin gently, insert the needle at a 90-degree angle, and hold still for 3 seconds. Allow the KwikPen to reach room temperature before injecting. Avoid injecting into bruised areas.
Should I stop Mounjaro if I develop bruising?
No. Minor injection site bruising does not require stopping treatment. Continue rotating sites and use proper injection technique. Speak to your prescriber if bruising is painful, persistent, or spreading. They may suggest adjustments to your injection routine.
Can I use Mounjaro if I take blood thinners?
Users of blood thinners (like warfarin or aspirin) may bruise more easily with any injection. Inform your prescriber about all medications before starting Mounjaro or Wegovy. They'll assess whether the medication is safe for you and advise on minimising bruising risk.
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