Ninety-four undergraduates were allowed to nominate freely causes of drug use. The 10 most frequently cited causes were placed on a matrix, and subjects were then asked to determine whether there was a cause-and-effect link between each pair of nominated causes. The composite matrix was then subjected to network analysis. The most frequently nominated causes were intrapersonal (i.e., addiction, stress, depression), although interpersonal (peer pressure) and environmental variables (easy access to drugs) were also significant. Network analysis gave rise to three distinct proximal causes of drug use: a disinhibitory motivational cause, a negative motivational cause, and a positive motivational cause. College students saw individual adjustment problems, along with peer pressure, as the temporally most immediate causes of drug use. 2 figures and 17 references