阿司匹林（英语：Aspirin），也称乙酰水杨酸（英语：acetylsalicylic acid），是水杨酸类药物，通常用作镇痛药、解热药和消炎药。 阿司匹林也能防止血小板在血管破损处凝集，有抗凝作用。长期低剂量服用可预防心脏病、中风与血栓。在心脏病发作后立即低剂量服用可降低下次心脏病发作或心肌梗死的风险。 该药还可有效预防多种癌症，特别是直肠癌。

阿司匹林的主要副作用是引起消化道溃疡、胃出血及耳鸣，尤其在高剂量服用时；不建议用于治疗或预防青少年或儿童的流感样症状或病毒性疾病，因为这会增加患瑞氏综合征的风险。

Aspirin, also known as acetylsalicylic acid (ASA), is a medication, often used to treat pain, fever, and inflammation. Aspirin is also used long-term, at low doses, to help prevent heart attacks, strokes, and blood clot formation in people at high risk of developing blood clots. Low doses of aspirin may be given immediately after a heart attack to reduce the risk of another heart attack or the death of heart tissue. Aspirin may be effective at preventing certain types of cancer, particularly colorectal cancer.