December 10, 2009

By Karla Gale

NEW YORK (Reuters Health) Dec 08 - Adolescents who use cannabis are at risk for depression as young adults, findings from a new study suggest.

"Some studies have shown a cross-sectional association between cannabis use and depression, but limited studies have attempted to demonstrate temporal association, especially among adolescents and young adults," Dr. Hon Ho, from the University of Colorado, Denver, told Reuters Health in an email.

Dr. Ho and his associates analyzed data from the National Longitudinal Study of Adolescent Health, a probability sample of adolescents in the US who were followed into young adulthood. The entire cohort included more than 21,000 subjects ages 11 to 21 at baseline. The group was about half male and half female, 52% Caucasian, 23% African American, 13% Hispanic, 2% Native American, and 8% Asian.

Dr. Ho presented the group's results this week in Los Angeles at the 20th annual meeting of the American Academy of Addiction Psychiatry.

All subjects were interviewed at baseline and again 1 and 6 years later. The mean ages at baseline and 6 years were 16.2 and 22.5 years, respectively.

To examine the temporal relationship between early cannabis use and later depression, the researchers looked at outcomes for subjects who did not have depression at baseline or the first follow-up (n = 9,803).

After adjusting for socioeconomic status, drug and alcohol use, age, gender, and race, prior cannabis use was a statistically significant predictor of later depression (odds ratio 1.27). Among subjects who had used cannabis more than 10 times, the odds ratio was 1.33, indicating a dose-dependent relationship.

"We also found current cannabis use was linked to depressive symptoms, consistent with other studies," Dr. Ho said.

A possible biological explanation for this association is that "receptors such as the cannabinoid receptors may act as moderators," he suggested. From a psychosocial standpoint, it's possible that a demotivating influence of cannabis could cause later dissatisfaction with progress in meeting goals, leading to depression.

Conversely, prior depression in the subjects who weren't using cannabis at the first two interviews (n = 7,521) was not linked with cannabis use at the 6-year follow-up.

"Psychoeducation is very important," Dr. Ho emphasized. "Drugs such as alcohol and marijuana may relieve depressed mood (and perhaps other medical problems) in the short-run, but patients should be encouraged to consider the long-term consequences of using such drugs."

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