Modified definition and source 1/1/2019
Level III Area of Specialization
Addiction (Substance Use Disorder)
A psychologist with a proficiency that involves the application of psychological treatment of addiction stemming from the use of alcohol and other psychoactive substances (e.g., nicotine, marijuana, cocaine, heroin) or behavioral addictions (e.g., gambling) with the aim of cessation or reduction of use and/or the amelioration of emotional, behavioral, interpersonal and other problems arising from the addictive behavior. Source: American Psychological Association, [1/1/2019: new definition]

Additional Resources: The APA proficiency is Addiction Psychology.