There is a great deal of confusion between "Stepping Stone Theory" and "Gateway Theory" in terms of understanding the evolution of drug and alcohol use across the life course. Stepping Stone Theory was developed in the 1950s and was based on flawed research. Incarcerated opiate users were asked if they had ever used cannabis. As most had, it was deduced that cannabis use inevitably led to involvement in what might be judged as harder substances.
Gateway Theory is a more sophisticated model. It posits that earlier and heavier involvement in cannabis use during the adolescent years leads to an increased probability of involvement in heavier and problematic usage in adult life. Therefore those who smoke cannabis at the age of 13 are more likely to progress through to heavier drug use than those who initiate use at 18.
A recent study by the University of Bristol has confirmed this Gateway pattern of involvement. The Avon Longitudinal Study of Parents and Children (ALSPAC) looked at levels of cannabis use during adolescence to determine whether these might predict other problematic substance misuse in early adulthood -by the age of 21- among 5,315 teens between the ages of 13 and 18. Assessed annually, these young people were categorised as non-user; occasional cannabis users (typically less than once a week); or frequent cannabis (typically once a week or more). In all, complete data were available for 1571 people. At the age of 21, they were asked to say whether and how much they smoked and drank, and whether they had taken other illicit drugs during the previous three months.
462 reported recent illicit drug use
176 (38%) had used cocaine
278 (60%) had used 'speed' (amphetamines)
136 (30%) had used inhalants
72 (16%) had used sedatives
105 (23%) had used hallucinogens
25 (6%) had used opioids
Male sex, mother's substance misuse and the child's smoking, drinking, and behavioural problems before the age of 13 were all strongly associated with cannabis use during adolescence. Other potentially influential factors were also considered: housing tenure; mum's education and number of children she had; her drinking and drug use; behavioural problems when the child was 11 and whether s/he had started smoking and/or drinking before the age of 13.
After taking account of other influential factors, teens who regularly used cannabis were 37 times more likely to be nicotine dependent and three times more likely to have a harmful drinking pattern than non-users. They were also 26 times more likely to use other illicit drugs. Both those who used cannabis occasionally early in adolescence and those who starting using it much later during the teenage years had a heightened risk of nicotine dependence, harmful drinking, and other illicit drug use. And the more cannabis they used the greater was the likelihood of nicotine dependence by the age of 21.
To read the full report, click here.