Substance use disorders describe the persistent use of drugs (including alcohol) despite substantial harm and adverse consequences. As you have learned in this module, substance use disorders are characterized by an array of mental/emotional, physical, and behavioral problems, such as chronic guilt, an inability to reduce or stop consuming the substance(s) despite repeated attempts, driving while intoxicated, and physiological withdrawal symptoms. Drug classes that are involved in substance use disorders include alcohol, caffeine, cannabis, phencyclidine and other hallucinogens, inhalants, opioids, sedatives, hypnotics or anxiolytics, stimulants, tobacco, and other or unknown substances. In the DSM-5 diagnosis of a substance use disorder, the severity of an individual’s substance use disorder is ranked as mild, moderate, or severe on the basis of how many of the 11 diagnostic criteria are met.

In 2017, 271 million people globally (5.5% of adults) were estimated to have used one or more illicit drugs. In 2017, substance use disorders from illicit substances directly resulted in 585,000 deaths. Direct deaths from drug use, other than alcohol, have increased over 60% from 2000 to 2015; alcohol use resulted in an additional three million deaths in 2016. For all these reasons and more, it is essential to know the criteria, risk factors, and treatment methods for substance abuse disorders.