A report titled Tobacco: The Smoking Gun issued by National Center on Addiction and Substance Abuse at Columbia University shows that teens who smoke cigarettes are more likely to drink alcohol and smoke marijuana than teens who do not smoke cigarettes. A press release and the full report are available from CASA. The implication, as you might guess from the title, is that tobacco use plays a role in leading teens to use these other drugs. They support this argument by noting that nicotine use effects the neurotransmitter receptor sites for dopamine and serotonin, two neurotransmitters involved in addiction and mood, respectively.
The numbers and science look pretty impressive, until you start to realize that this is all correlational data. When asked by Will Dunham of Reuters if smoking causes teens to abuse other drugs, former health secretary and head of CASA Joseph Califano had to admit “the jury is probably still out.”
Here is why this research does not deliver a clear verdict on cause and effect: A correlation shows a relationship between two variables. There are always multiple possible cause and effect relationships that could explain the relationship. An easy way to think about the possibilities is that X could cause Y, Y could cause X, or some other variable, Z could cause X and Y. In this case, we should wonder, for example, if nicotine causes marijuana use, or is it the other way around. And given what we know about individual differences in susceptibility to alcoholism and other addictions, we should certainly consider the possibility that these differences make some people more likely to use any and all of the substances they discuss.
There is no question that smoking is addictive and bad for you. But I’m not sure this report really does anything to further our understanding of the relationship between smoking and using other addictive drugs. Maybe it will spur somebody on to try a more clever research design.