Many drug addicts take not only one substance but rather several. Scientists at the Max Planck Institute of Experimental Medicine in Göttingen have investigated the role that genes and the environment play in the development of such multiple substance consumption or polytoxicomania. Their results show that, in addition to genetic factors, the accumulation of several unfavorable environmental factors causes people to slip into such an extreme form of multiple drug use. Among the risk factors were sexual and physical abuse, living in a big city, and migration experience as well as the use of cannabis and alcohol before age of 18 years. Cannabis and alcohol may act as gateway drugs for vulnerable individuals, thereby paving the way to more problematic substance use.