A 1994 report from the Center on Addiction and Substance Abuse at Columbia University, found a correlation between the use of cigarettes and alcohol and the subsequent use of cannabis.
The report asserted a link between alcohol and cannabis use and the subsequent use of illicit drugs like cocaine.
[1] It found that when younger children used, the more often they use them, the more likely they were to use cocaine, heroin, hallucinogens and other illicit drugs.
the experiments permitted concrete conclusions on the underlying molecular biological alteration in the brain.
[4] The biological changes in mice correspond to the epidemiological observations in humans that nicotine consumption is coupled to an increased probability of later use of cocaine.