A drug that can reverse the effects of opioid overdose and can be lifesaving if administered in time. The drug is sold under the brand name Narcan or Evzio.

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

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.”