Friendship Intimacy, Close Friend Drug Use, and Self-Medication in Adolescence.

The current study examined between- and within-person processes related to friendship intimacy, close-friend substance use, negative affect, and self-medication. We tested between-person hypotheses that global negative affect, friendship intimacy, and close-friend drug use predict increased substance use, and the within-person hypothesis that friendship intimacy and close-friend substance use moderate the temporal relationship between daily negative affect and subsequent substance use (i.e., self-medication). Experience sampling methodology (ESM) was employed to capture daily variations in mood and substance use, and multilevel modeling techniques were used to parse between- versus within-person differences in risk for use. Findings supported between-person hypotheses that higher levels of negative affect and lower levels of friendship intimacy predicted greater substance use, and a consistent trend indicated that friendship intimacy and close-friend drug use interact to predict substance use more generally (though not for self-medication). Risk and protective mechanisms emerged from this interaction such that the effect of friendship intimacy on adolescent use depends on the degree of close-friend drug use. More specific reformulations of the risk processes involving friendships and self-medication among younger youth are indicated.