Adverse reactions can be especially dangerous if a medication error occurs in a patient who’s receiving a high-alert drug.The sickest patients—those in the intensive care unit—typically receive anywhere from 20 to 40 different drugs.These patients are the most vulnerable to adverse reactions,drug interactions,and life-threatening consequences of a medication error.In this section,we list the most commonly reported adverse reactions by body system.Life-threatening reactions appear in boldface.