n. acetylsalicylic acid: the most commonly used nonopioid analgesic, which also has antipyretic and anti-inflammatory properties as well as the ability to prevent the formation of blood clots. Aspirin alleviates pain by peripheral mechanisms. In controlling fever, it acts on the body's thermoregulatory center in the hypothalamus, which therefore reduces body temperature. Adverse effects of overuse include gastric irritation or ulceration with bleeding. Over dosage affects the central nervous system and other body systems in a negative way.