Order of onset of substance abuse and depression in a sample of depressed outpatients.

Drug abuse has been thought to cause depression, or to serve as a form of self-medication for depression. Our objective was to examine whether specific types of drug abuse preceded or followed the onset of depression. A retrospective, blinded case-controlled assessment of the drug and depressive history of depressed outpatients was conducted. Three hundred seventy-five patients with major depressive disorder were evaluated for comorbid drug dependence using the Structured Clinical Interview for DSM-III-R (SCID). They were selected from the psychiatric outpatient department of a metropolitan teaching hospital and grouped into homogeneous classes of drug dependence including alcohol, cannabis, cocaine, amphetamine, LSD, hypnosedative, opiate, and polysubstance use. We determined the percent of depressed patients with each specific type of drug abuse, their age of onset of depression and onset of specific drug abuse, and the mean number of lifetime depressive episodes for each patient. We found that alcohol dependence followed the onset of first life depression by 4.7 years (P = .02, two-tailed). Among polydrug-dependent patients, each drug abused followed the onset of depression, except for LSD, which coincided with the onset of depression. Among polydrug users, cocaine dependence occurred 6.8 years after the first major depressive episode (P = .007) and alcohol dependence 4.5 years after the onset of depression (P = .007). Opiate and sedative users had the least number of lifetime depressive episodes (3.7), and LSD and cocaine users had the greatest number (12.2). We conclude that alcohol and cocaine use in this sample of depressed outpatients conformed to a pattern of self-medication.