The Substance-Related Disorders include disorders related to the taking of a drug of abuse (including alcohol), to the side effects of a medication, and to toxin exposure. In this manual, the term substance can refer to a drug of abuse, a medication, or a toxin. The substances discussed in this section are grouped into 11 classes: alcohol; amphetamine or similarly acting sympathomimetics; caffeine; cannabis; cocaine; hallucinogens; inhalants; nicotine; opioids; phencyclidine (PCP) or similarly acting arylcyclohexylamines; and sedatives, hypnotics, or anxiolytics. Although these 11 classes appear in alphabetical order, the following classes share similar features: alcohol shares features with the sedatives, hypnotics, and anxiolytics; and cocaine shares features with amphetamines or similarly acting sympathomimetics. Also included in this section are Polysubstance Dependence and Other or Unknown Substance–Related Disorders (which include most disorders related to medications or toxins).