The preferred term is substance use disorder. When referring to opioids, see the Opioid Use Disorder (OUD) definition below and text box discussing the difference between “tolerance,” “dependence,” and “addiction.”

The use of illegal drugs and/or the use of prescription drugs in a manner other than as directed by a doctor, such as use in greater amounts, more often, or longer than told to take a drug or using someone else’s prescription

Adaptation to a drug that produces symptoms of withdrawal when the drug is stopped.