Substance abuse, also known as drug abuse, is the use of a drug in amounts or by methods which are harmful to the individual or others. It is a form of substance-related disordersubstance-related disorderSubstance-induced disorders include medical conditions that can be directly attributed to the use of a substance. These conditions include intoxication, withdrawal, substance-induced delirium, substance-induced psychosis, and substance-induced mood disorders.Substance-related disorder . Differing definitions of drug abuse are used in public health, medical and criminal justice contexts.