Applying an Extended Version of the Theory of Planned Behavior to Illicit Drug Use Among Students¹

Abstract

This study employed the theory of planned behavior (TPB) to investigate the factors underlying intentions to use and use of LSD, amphetamine, cannabis, and ecstasy over 6 months in a sample of students ( N = 461). The TPB provided good predictions of both intentions (mean R 2 = .49) and behavior (mean R 2 = .45). Descriptive norms explained additional variance in intentions for all the drugs, and moral norms explained additional variance in cannabis intentions. Attitude variability moderated the impact of attitudes on intentions for LSD ( p < .10) and ecstasy ( p < .05). Attitude moderated the impact of perceived behavioral control (PBC) on intentions for all drugs ( p < .001). PBC moderated the impact of intentions on behavior for LSD ( p < .05), amphetamine ( p < .10), cannabis ( p < .05), and ecstasy ( p < .10). These interaction effects elucidate limiting conditions among the variables in the TPB.