Can aspirin (acetylsalicylic acid) cause bruising?

From the Guidelines

Yes, aspirin (acetylsalicylic acid) can cause bruising. This common side effect occurs because aspirin inhibits platelet function by irreversibly blocking the enzyme cyclooxygenase-1 (COX-1), which prevents platelets from producing thromboxane A2, a substance that helps platelets stick together to form clots. With reduced clotting ability, even minor trauma to blood vessels can lead to more bleeding under the skin, appearing as bruises (ecchymoses).

Key Points to Consider

• The risk of bruising increases with higher doses and longer duration of use, as reported in studies such as 1 and 1.
• People taking daily aspirin therapy (typically 81-325 mg) for heart attack or stroke prevention may notice more frequent or larger bruises than usual.
• This effect on platelets lasts for the entire lifespan of the affected platelets (about 7-10 days), which is why doctors recommend stopping aspirin 5-7 days before surgical procedures, as noted in 1.
• If you experience unusual or severe bruising while taking aspirin, you should consult your healthcare provider, as it could indicate an underlying bleeding disorder or interaction with other medications that also affect blood clotting.

Important Considerations

• Aspirin use is associated with a significant reduction in cardiovascular events, but it also increases the risk for major bleeding events in men and women, as discussed in 1 and 1.
• The WHS reported that gastrointestinal bleeding, peptic ulcers, self-reported hematuria, easy bruising, and epistaxis were significantly more common in women assigned to aspirin therapy than in women assigned to placebo, highlighting the need for careful consideration of the risks and benefits of aspirin therapy.
• Regular use of nonsteroidal anti-inflammatory drugs may increase the risk for chronic renal disease and may impair blood pressure control in hypertensive patients, but a low dose of aspirin is a very weak inhibitor of renal prostaglandin synthesis and has no clinically significant effects, as noted in 1.

From the FDA Drug Label

Stomach bleeding warning: This product contains an NSAID, which may cause severe stomach bleeding The chance is higher if you... Take a blood thinning (Anticogulant) or steroid drug

Aspirin can cause bleeding which may lead to bruising.

• Key words: bleeding, bruising, NSAID, blood thinning, Anticogulant The FDA drug label for aspirin 2 suggests that aspirin may increase the risk of bruising due to its effect on bleeding, especially when taken with other medications such as blood thinners.

From the Research

Aspirin and Bruising

• Aspirin (acetylsalicylic acid) can cause bruising due to its antiplatelet effects, which inhibit platelet function and increase the risk of bleeding 3, 4.
• The antithrombotic action of aspirin is due to the inhibition of platelet cyclooxygenase (COX) at the functionally important amino acid serine529, preventing the access of the substrate (arachidonic acid) to the catalytic site of the enzyme at tyrosine385, resulting in an irreversible inhibition of platelet-dependent thromboxane formation 3.
• Any effective antiplatelet dose of aspirin is associated with an increased risk of bleeding, and the individual benefit/risk ratio determines the administration of the compound 3.
• Aspirin exerts its effects by irreversibly blocking cyclooxygenase, and therefore, its actions persist for the circulating lifetime of the platelet, producing a systemic bleeding tendency by impairing thromboxane-dependent platelet aggregation and consequently prolonging the bleeding time 4.

Mechanisms of Aspirin-Induced Bruising

• Aspirin inhibits platelet function independent of the acetylation of cyclo-oxygenase, and higher doses of aspirin may have additional antithrombotic effects 5.
• The clinical risks of bleeding with aspirin are enhanced by the concomitant use of alcohol or anticoagulants and by associated conditions, including advanced age, liver disease, and other coexisting coagulopathies 4.
• Aspirin resistance, as measured in vitro, is the inability of aspirin to reduce platelet activation and aggregation by failure to suppress the platelet production of thromboxane A2, and possible causes of aspirin resistance include poor compliance, inadequate dose, drug interactions, genetic polymorphisms of cyclooxygenase-1, increased platelet turnover, and upregulation of non-platelet pathways of thromboxane production 6.

Clinical Implications

• The clinical implication of aspirin resistance has not yet been elucidated via prospective trials that have controlled for confounders, such as hypertension, diabetes, and dyslipidemia 6.
• Large meta-analyses have found low-dose aspirin to be as effective as high-dose aspirin in preventing vascular events, making a dose-dependent improvement in laboratory response clinically irrelevant 6.
• Further research exploring the mechanisms of aspirin resistance is needed in order to better define aspirin resistance, as well as to develop a standardized laboratory test that is specific and reliable, and can correlate with the clinical risk of vascular events 6.