Comorbidity of bipolar disorder and substance abuse in Costa Rica: pedigree- and population-based studies

Background: The purpose of this study was to determine the prevalence of substance use disorders (substance abuse or substance dependence: SA/SD) in a large sample of Bipolar Type I (BPI) patients drawn from the Costa Rican population and to describe the effects of SA/SD on the course of their bipolar disorder. Method: 110 subjects from two high-risk (for BPI) Costa Rican pedigrees and 205 unrelated Costa Rican BPI subjects were assessed using structured interviews and a best estimate process. χ2 and survival analyses were performed to assess the effect of gender on comorbidity risk, and the effect of comorbidity on the clinical course of BPI. Results: SA/SD (primarily alcohol dependence) occurred in 17% of the BPI patients from the population sample and 35% of the BPI patients from the pedigree sample. Comorbid SA/SD was strongly associated with gender χ2=16.84, P=0.00004). In comorbid subjects, alcohol dependence tended to predate the first manic episode (χ2=6.54, P<0.025). History of SA/SD did not significantly alter the prevalence of psychosis or age of onset of mania in BPI subjects. Conclusions: These results suggest that SA/SD comorbidity rates are lower in this type of population than in BPI patient populations in the US. Gender is a strong predictor of comorbidity prevalence in BPI patients from this population. Although SA/SD may be a risk factor for precipitating BPI in those at risk, in this population comorbid BPI subjects do not have a different onset or course of BPI in comparison to BPI patients without comorbidity.