I was rather surprised to find that a Google search for: marijuana gateway drug, found very few anti-drug sites claiming the use of marijuana consequently results in the use of harder illicit drugs.

Rather there appears to be an abundance of sites outright rejecting these claims or shifting the blame, arguing tobacco and alcohol are the real gateway drugs. Though amidst arguments from advocates/opponents of the gateway theory, there still remains a missing piece of the puzzle.

Firstly, it is important to acknowledge that there is a relationship between marijuana and later illicit drug use. Second, research indicates that marijuana users are up to two times more likely to use other illicit substances than non-marijuana users.

It is thereby quite easy to conclude that marijuana is the cause of later drug use. However there is a rather large flaw in the validity of this conclusion (and much of the research on the gateway theory). That is, that one event preceding another does NOT indicate causality.

The missing aspect in this whole debate, to which I made reference earlier, seems to be the word ‘how’. I’ve found that on the webpage’s I’ve come across, people are far too happy to say “research/statistics show…therefore, end of story”.

The goal of research and statistics should be to seek understanding. Instead of asking: is marijuana a gateway drug? We should be asking questions like: If marijuana is a gateway drug, by what mechanism does it encourage later illicit drug use? Or, If Marijuana is not causing later drug use then how can we explain the relationship between the two?

One group of researchers conducted a study on the gateway theory and offered an interesting thought as to explain the relationship between marijuana and later drug use. They suggested that individuals may posses an genetic propensity to use drugs, and that given marijuanas comparative acceptability and availability compared to other drugs,  it is for lack of a better term ‘chosen’ first by those who are already likely to use illicit drugs3. 

Concerning the availability of Marijuana in Australia, the 2007 National Drug Strategy Household Survey found that 17.1% of the population aged over 14 years had been offered or has had the opportunity to use Marijuana. That compared with 8.1% for ecstasy, 4.9% for methamphetamine, 3.9% for cocaine and 0.9% for heroin. In addition, it is likely that though increased association with Marijuana users, individuals may meet other drug users, which may thereby increase ones opportunity to obtain otherwise unavailable drugs.

So there we have it, an alternative and plausible explanation for the known relationship between marijuana and subsequent drug use. Also, in my opinion a perfect example of how easy it is to jump to conclusions on an issue as topical as drug use. In reading this I urge you to not to accept anything at face value. Look for evidence. I’m not saying the theory here is a definitive explanation of the gateway effect, but it’s certainly a start.

References

1. Fergusson, D. M., Boden, J. M., & Horwood, L. J. (2006). Cannabis use and other illicit drug use: testing the cannabis gateway hypothesis. Addiction, 101, 556-569.

2. Lessem, J. M., Hopfer, C. J., Haberstick, B. C., Timberlake D., Ehringer, M. A., Smolen, A., & Hewitt, J. K. (2006). Relationship between Adolescent Marijuana Use and Young Adult Illicit Drug Use. Behaviour Genetics, 64(4), 498-506.

3. Cleveland, H. H. & Wiebe, R. P. (2008). Understanding the association between marijuana use and later serious drug use: Gateway effect or developmental trajectory? Development and Psychopathology, 20, 615-632.

4. Australian Institute of Health and Welfare. (2008). 2007 National Drug Strategy Household Survey: first results. Drug Statistics Series number 20. Cat. no. PHE 98. Canberra: AIHW.