Stating a relative risk without giving a clear idea what it is in relation to is almost completely meaningless. For example, telling you that I was going to increase the amount of money you have in your pocket right now by 500% sounds exciting, right? Well it actually IS exciting if you have $1,000 but it’s a real yawner if you have only 5 cents. In reality, this study is a real yawner.

Here is some idea of the absolute risks and some real perspective on this study. The study authors do mention that statistically, marijuana use may lead to 800 additional cases of psychotic illness because of marijuana’s “wide popularity.”

According to a 2005 survey, 97.5 million Americans ages 12 or older have tried marijuana at least once. Assuming that the authors were only referring to these US numbers then 800 is about 0.0000000000006% of 97.5 million or 1 in 122,000 odds. In contrast, your lifetime odds of dying in a motor vehicle accident are 1 in 237. In fact, your risk of developing psychosis from smoking a single joint is two times less likely than your odds of getting legally executed here in the US (one in 62,000)! Even for chronic marijuana users where the relative risk of developing a psychotic illness is up to 200% higher, the odds and absolute risks remain ridiculously small.

The prevalence of schizophrenia (one of the major causes of psychosis) is very small at 1.1% or 2.2 Million people in the US. Based on these numbers you are statistically MORE likely to develop schizophrenia if you DON’T smoke marijuana than if you do. This is because other factors such as a family history of schizophrenia and infections during pregnancy have much higher odds ratios for schizophrenia than marijuana use.

The study in question is a meta-analysis of 35 other longitudinal population based studies. What this means is that these studies followed a certain number of people who smoked pot to see how many developed psychosis. The control group was the general population. This is problematic since any general population does not tend to be exactly like or necessarily similar to populations that use marijuana.

Another limitation of this study is in evaluating causality. It’s the chicken or the egg dilemma. Simply put, people at risk for psychotic illness may be more likely to use marijuana. For example, those other schizophrenia risk factors (family history, fetal infections, low birth weight, being born in an urban environment) may themselves be associated with an increased rate of marijuana use.

Or since psychiatric illness tends to be under-reported, many of the subjects in these studies may have already been suffering from a psychotic illness and had been “self-medicating” with marijuana or other substances before being formally diagnosed. This is not a small problem when it comes to studying psychiatric illness and substance abuse. Schizophrenics in particular have a 47% increased lifetime rate of substance abuse or dependence including marijuana. Teasing out which came first or what is causing what can be extremely difficult.

When compared to the total number of deaths (in the hundreds of thousands annually) directly attributed to the use of legal substances like alcohol and tobacco, the tiny association of psychotic illness with marijuana use found in this study hardly seems worthy of all the attention. And yet there are over 500 news articles about this story referenced on Google.

The problem that comes from such non-substantive crap is evidenced by the following all-too-common degeneration of logic.

The Study: There may be a small association between marijuana use and later development of psychotic illness however we can’t yet prove a direct link.

The Media: “Marijuana may increase psychosis risk.”

The general population: “If you smoke pot you might go crazy!”

Conservative Carnival Barkers : ” Look at this. It looks like reefer madness is real, or it can be.”

Self-Serving Politicians: “Don’t legalize marijuana! It’s bad for you!”

And so the reefer madness propaganda machine marches on.

Ironically the news from this study could have easily been spun in a very positive light. The study found no hard evidence that marijuana use is associated with increased rates of depression, anxiety disorders, or suicidal tendencies. This is significant as these conditions are far more common in the general population than psychotic conditions. Taken as a whole and at least from a psychiatric perspective, marijuana use appears to be very safe . . certainly safer than most antidepressant medications! So put that in your pipe . . er . . bong and smoke it!