Dopamine receptor (D4) polymorphism is related to comorbidity between marijuana abuse and depression

The rates of marijuana abuse are steadily increasing in the U.S. Data suggest that comorbid marijuana abuse and depression is associated with worse outcomes than either diagnosis. Genetic studies independently link the DRD4 gene polymorphism to substance use and to internalizing disorders, but no study has examined whether the DRD4 polymorphism is linked to comorbid marijuana use and depression in a population sample. This study examined associations between the DRD4 gene 48 bp VNTR polymorphism and comorbidity between marijuana use frequency and depression in a diverse, non-clinical adolescent sample (n = 1882; ages 14 to 18) from the National Longitudinal Study of Adolescent Health (Add Health). Multinomial regression analyses indicated that the odds of being comorbid for depressive symptoms and marijuana use are approximately 2.5 ≥ with the ≥ 7R/≥ 7R genotype than youths who carry the < 7R/< 7R genotype, controlling for the effects of ethnicity, gender, age, violent victimization, and alcohol related problems. Findings provide genetic clues for psychopathology characterized by prominent externalizing and internalizing features.