The possibility of a causal link between tobacco use and psychosis does not merit further examination

Following my previous post, yet another article on the association between smoking and psychosis has been published in The Lancet Psychiatry. Usefully the article makes reference to the Bradford Hill criteria for deciding whether an association should be interpreted as causal. It suggests that the association is plausibly causal because nicotine may increase dopamine consistent with the excess striatal dopamine theory of schizophrenia. Trouble is that efforts to validate the dopamine theory of schizophrenia empirically have failed (Kendler & Schaffner, 2011).

As the comment in the same issue of The Lancet Psychiatry says, "The most likely explanation ... is that cigarette smoking is associated with an increased risk for schizophrenia." Factors in the social environment, such as family history, urban environment and childhood adversity, are associated with both smoking and psychosis. A social environmental explanation of both psychosis and smoking is much more plausible than a biochemical explanation that the empirical evidence contradicts.