Can smoking pot make you smarter?

Is it possible that if you have schizophrenia, smoking marijuana will actually improve your cognitive performance? Since this blog is often concerned with the relationship between science and its communication,...

Is it possible that if you have schizophrenia, smoking marijuana will actually improve your cognitive performance?

Since this blog is often concerned with the relationship between science and its communication, something which has come up once or twice here is the way drug and alcohol research is reported in the media.

Very often, it is reported that marijuana use causes schizophrenia and psychosis. This is despite the fact that there is quite strong evidence that it does not do so.

We also see government campaigns presenting very misleading information about marijuana and its effects.  Consider this one stating that “Cannabis can leave you permanently out of it”.

So it was not surprising this week, when we did not see headlines such as “Marijuana makes schizophrenics smarter,” even though there was some interesting research possibly suggesting exactly that.

But what’s really interesting about this research is that it seems to suggest that not only does smoking marijuana make people with schizophrenia smarter, it seems to show that the more often you smoke, and the younger you start, the smarter you get. (Yes, there are also other interpretations of the data. Continue reading.)

The researchers did two things: a meta-analysis and an experimental study. They found 10 studies that looked at the cognitive performance of people with schizophrenia who smoked marijuana and found a remarkable homogeneity between the studies.

Together, these 11 studies (the 10 in the analysis and the 1 they performed) found that people who had schizophrenia, and had a history of smoking marijuana, had a better visual memory as well as better planning and reasoning than their non-using peers. For several domains, there were no differences between the groups but for no domain, were the non-using groups better than the using groups.

Additionally, they found that a higher frequency of smoking was associated with higher cognitive performance, as was earlier age of smoking onset. (In their own study, the association was only present for people who started smoking before they were 17.)

How could these findings possibly be explained?

Well, of course one option is that smoking marijuana causes the better performance. This is plausible since it is known that people with schizophrenia and psychosis tend to have poorer cognitive performance and so something like marijuana might perform what the authors call “a neuroprotective role”. That is, the cognitive deficits that become apparent in people with schizophrenia at around puberty might be avoided if they smoke marijuana before, or at, that age.

However, there is another explanation of the data suggested by the authors that turns on the question raised earlier: does marijuana cause psychosis? If it does cause psychosis, the researchers suggested that there might be a group of people who would not have developed schizophrenia if they had not smoked marijuana. And that group of people, as a group less prone to schizophrenia, might also be less cognitively impaired. So people who have a history of marijuana would be more likely be a group that is less prone to schizophrenia and therefore perhaps have better cognitive performance.

So should people who think they might be schizophrenic go out and smoke lots of dope? Clearly not. While it seems to me that the evidence stands against the hypothesis that pot causes schizophrenia, the matter is far from closed and a lot of researchers do think there is such a link. Moreover, this latest research is not based on an awful lot of data and really needs to be replicated in larger studies.

What’s the bet, however, that the government website “” won’t mention this new and interesting research? Much better, they think, to stick with skewed, misleading messages rather than provide believable, balanced evidence from which people can make informed decisions.

[Via me at Psychiatry Update] Yücel M, Bora E, Lubman DI, Solowij N, Brewer WJ, Cotton SM, Conus P, Takagi MJ, Fornito A, Wood SJ, McGorry PD, & Pantelis C (2010). The Impact of Cannabis Use on Cognitive Functioning in Patients With Schizophrenia: A Meta-analysis of Existing Findings and New Data in a First-Episode Sample. Schizophrenia bulletin PMID: 20660494 Frisher, M., Crome, I., Martino, O., & Croft, P. (2009). Assessing the impact of cannabis use on trends in diagnosed schizophrenia in the United Kingdom from 1996 to 2005 Schizophrenia Research, 113 (2-3), 123-128 DOI: 10.1016/j.schres.2009.05.031