This month data published from a significant French study¹ has confirmed more than three decades of research pointing to the fact that cannabis use is a strong contributor to other illicit drug use. The study specifically looked at cannabis use patterns on the initiation into other drugs – otherwise known as the ‘gateway’ theory.

In their study, Cannabis use stages as predictors of subsequent initiation with other illicit drugs among French adolescents: use of a multi-state model; Addictive Behaviours, researchers Mayet, Legley, Falissard and Chau, reconstituted a nationwide retrospective cohort on drug use  on 29,393 teenagers. ‘

A Markov multi-state model was fitted, modeling all possible pathways from initial abstinence to cannabis initiation, daily cannabis use and OID (Other Illicit Drug) initiation. The model was adjusted for tobacco and alcohol use. The risk for OID initiation appeared 21 times higher among cannabis experimenters and 124 times higher among daily cannabis users than among non-users. Tobacco and alcohol use were associated with a greater risk of moving on to cannabis initiation (hazard ratio (HR)=1.2 for tobacco initiation, HR=2.6 for daily tobacco use and HR=2.8 for drunkenness initiation). The results of this study provide a confirmation of a stage process in drug use, mediated by cannabis and liable to lead to OID experiment.

This is compatible with the literature on the gateway theory, but goes further by modelling the entire sequence of use. OID experiment could be a consequence of initial opportunity to use the more accessible illicit drug, cannabis’.

The evidence points to the key issue in all this as being the age of onset of use. The vast majority of demographic data emerging across most societies is revealing that tobacco, alcohol and cannabis use are all and almost always, initiated in early to late adolescence.

 The French study also reports:
‘…the influence of early initiation appears very deleterious because it is liable to compromise cognitive learning, to be linked with psychiatric disorders or to lead to social problems like truancy or delinquency. Thus adults aged over 25 who initiated cannabis use before the age of 15 report a lifetime use of cocaine in 62% of cases, a lifetime use of heroin in 9% of cases, and abuse of psychoactive medication in 54% of cases. These percentages appear to be much higher than those observed in the general population.’

Jo Baxter, Executive Officer, Drug Free Australia said: “The gateway or initiation into illicit drug use has been referred to for more than three decades as a progression, known as ‘Gateway Theory’, first affirmed after studies on teenagers were conducted and findings published in 1975, by Professor Denise Kandel of Columbia University and updated the results on patterns of drug use on the same cohort, in 1984. The results were published in a series of articles in the American Journal of Public Health in 1984.

In the 1990's (5th edition) of Keep Off the Grass, researcher, Gabriel Nahas summarised the evidence supporting the theory connecting marijuana use to other illicit drug use.
"Marijuana users are sixty-six times more likely to use cocaine subsequently than subjects who have never consumed marijuana".
 
Despite the unscientific approach taken by those who support a pro-drug stance on cannabis, the long standing evidence is now very clear – The Gateway Path exists -  and our young are the victims’, said Ms Baxter. 

Reference:

1. Mayet A, Legleye S, Falissard B, Chau N.; Cannabis use stages as predictors of subsequent initiation with other illicit drugs among French adolescents: use of a multi-state model; Addictive Behaviours. (soft release Jan 12)2012 Feb; 37(2):160-6. Epub 2011 Sep 17.