Addiction (substance use disorder) exists when a person exhibits two or more of the following symptoms: (1) impaired control, (2) social problems, (3) risky use, and (4) physical dependence.

Impaired control means using more of a substance or more often than intended; or wanting to cut down or stop use but not being able to.

Social problems includes things like neglecting responsibilities and relationships, abandoning activities the person used to care about, or failing to fulfill obligations at home, school or work - because of the substance use.

Risky use includes things like using in risky settings, continued use despite known problems, engaging in risky substance-related practices like sharing needles, risky sexual activity (because of, or in order to obtain the drug), and driving while intoxicated.

Physical dependence is needing more of the substance to get the same effect, or having withdrawal symptoms when a substance isn't used.

Two or three symptoms indicate mild substance use disorder. Four or five symptoms indicate moderate, and six or more indicate severe substance use disorder. When people talk about addiction, they are typically referring to severe substance use disorder.

Physical dependence and tolerance are not the same as addiction. Substance use disorder is by definition problematic.