All these studies required that subjects agree to participate in surveys and relied on their ability to accurately recall and report their drug abuse, an illegal behavior. In this study, we examine official criminal and medical records on cannabis, stimulant (including cocaine) and sedative abuse in twins and full siblings in a Swedish nationwide male sample. We fit multivariate models that permit us to determine the degree to which genetic and environmental risk factors are shared versus specific across abuse of these three major classes of psychoactive substances.
