The research in favor of gateway theory
To check the gateway hypothesis there was a long, ten-year investigation in the State of Victoria, Australia. There was a stratified, random sample involving 1,943 adolescents studying at secondary schools across the state. The age group was 14-15 years. The participants were followed up till they reached 24-25 years of age, and interviewed eight times within these years. It was revealed that at the age of 24, 12 percent of the interviewees had used amphetamines the year before, with 1%”“2% using at least weekly. The use of amphetamine among young adults was strictly associated with the use of other drugs in adolescence and consequent dependence in young adulthood. Using cannabis at the age of 20 was very likely to result in using amphetamines at the age of 20. “Those who were smoking cannabis at the age of 15 were as much as 15 times more likely to be using amphetamines in their early 20s,”¯ Louisa Degenhardt (2007, 1278) provides.
Another study was conducted by the scholars of the Virginia Commonwealth University. The researchers had the intention to distinguish how those who had used cannabis were influenced by the contribution of (a) genetic, (b) shared environmental and (c) unique environmental influences on further development of their dependence on other drugs. As Arpana Agrawal with colleagues (2004, 1234) have estimated, “while cannabis was strongly predictive of use of other drugs in the future, the main contributors to this effect were the shared environmental and genetic risk for all substances.”¯ In some cases there were causal influences revealed, which makes the gateway theory sound operative, but still not the decisive base for association between the effect and the use of marijuana.
One more laboratory research was a study of rats at the Karolinska Institute in Sweden (2006). The scientists involved 12 rats with the goal to find out how adolescent use of cannabis may affect the subsequent abuse of other illicit drugs. As for the adolescence of rats, these were “teenage”¯ individuals, 28-49 days old, which is equal to 7-11 human years. The experimental animals were given small doses of tetrahydrocannabinol (THC), the psychoactive substance appearing in marijuana, almost equivalent to one cannabis cigarette. The dose was given to a rat every three days, and then the rats were free to take heroin by pushing a lever. The study revealed that the rats having tasted THC took greater doses of heroin (Ellgren, Spano & Hurd 2006, 614). Further on, they studied how the brain cells were affected and found out that THC changes the opioid system associated with positive emotions. Consequently, the effects of opiates are lessened and the rates begin to need more heroin. Hence, Ellgren, Spano & Hurd (2006, 615) conclude that their findings “support the gateway hypothesis demonstrating that adolescence cannabis exposure has an enduring impact on hedonic processing resulting in enhanced opiate intake, possibly as a consequence of alterations in limbic opioid neuronal populations.”¯ However, the analysis has been criticized. For example, Paul Armentano, policy analyst for the National Organization for the Reform of Marijuana Laws, argued that the conclusions made on the rats given THC at such a young age of 28 days, it was not possible to extrapolate the results to humans. What is more, other similar tests conducted on animals did not prove the correlation.