The gateway hypothesis holds that drug users start off with alcohol and tobacco, move on to cannabis and then on to other illegal drugs. People who depart from this sequence of drug use are thought to be at an increased risk of long-term dependence. However, the 'market' for illegal drugs has changed considerably since the gateway hypothesis was developed and researchers in New Zealand looked at a sample of 12,992 people to see if it still held true. Only 2.6% of the sample departed from the sequence of drug use outlined in the gateway hypothesis. Use of other illicit drugs before cannabis was the most common departure found in 2.3% of alcohol users, 3% of cannabis users, 8.6% of cocaine users and 16.7% for those who had used other illicit drugs. Use of other illicit drugs before cannabis was more predominant in younger cohorts and those with more early-onset anxiety and depression. Once all the other factors had been taken into account people who departed from the gateway sequence were no more likely to develop drug dependence. Depression, anxiety and early-onset bipolar disorder were all more likely to increase the risk of drug dependence.
Well, J. Elisabeth and McGee, Magnus A. - Violations of the usual sequence of drug initiation: prevalence and associations with the development of dependence in the New Zealand Mental Health Survey Journal of Studies on Alcohol and Drugs November 2008, 69(6), 789-795