Major Findings: The relative risk for depression after any cannabis use was 1.27, compared with nonusers, and 1.33 after use on 10 or more occasions.
Data Source: National Longitudinal Study of Adolescent Health involving more than 21,000 subjects.
Disclosures: The researchers received federal funding for the study. They reported no financial conflicts of interest.
LOS ANGELES — Cannabis use in adolescence was associated with the subsequent development of depression, but the reverse did not prove to be true in a large, longitudinal study presented at the annual meeting of the American Academy of Addiction Psychiatry.
Dr. Hon Ho and associates from the department of psychiatry at the University of Colorado, Denver, examined data from the National Longitudinal Study of Adolescent Health, a national probability sample of individuals who were surveyed several times over a 14-year period on social, economic, psychological, and medical topics.
The sample included 10,778 female and 10,519 male participants who were between the ages of 11 and 21 years in the mid-1990s, when the first and second waves of interviews were conducted.
About half the sample was white; 23% was African American; 13%, Hispanic, 8%, Asian, and 2%, Native American.
The median age at Wave 1 was 16, and at Wave 3 (during 2001-2002) the median age was 22.
Dr. Ho combined responses from Waves 1 and 2, which represented only a few years (1994-1996) and then tracked temporal patterns between first stated use of cannabis and the first indicator of depression based on the Center for Epidemiologic Studies–Depression (CES-D) scale.
Prior cannabis use proved to be a statistically significant predictor of later depression after adjustment for age, sex, race, socioeconomic status, and drug and alcohol use.
The relative risk for depression after any cannabis use was 1.27 (95% confidence interval 1.07-1.49), compared with nonusers. That risk increased to 1.33 (1.07-1.64) among people who reported using cannabis on 10 or more occasions.
Low socioeconomic status and black, Native American, or Asian race were also predictive of later depression; being male was a protective factor, reported Dr. Ho in an oral presentation of his paper.
The investigators then examined the reverse scenario: depression at Waves 1 or 2 and subsequent cannabis use at Wave 3, but found no significant temporal relationship.
“Depression did not seem to increase risk of cannabis use at a later time,” he said.
Dr. Ho said that the large sample size was a strength of his study, but reliance on self-reported behaviors and the lack of more precise dose information about cannabis use compromised the study's ability to determine causality, rather than a mere association.
Nonetheless, the findings do have some policy and practice implications, particularly as local governments consider easing restrictions on marijuana purchasing and use for medicinal purposes, he said.
The fact that early cannabis use is associated with later depression is “definitely something we want to consider,” both societally and in counseling of adolescents and families, he said.
Prior cannabis use proved to be a statistically significant predictor of later depression.
Source DR. HO