[Music] even as proponents of cannabis legalization contend that marijuana is a harmless natural substance that improves quality of life a growing body of evidence links it in a small but significant number of users to the induction or aggravation of psychosis psychotic disorders are arguably the most serious of mental illnesses the best-known being schizophrenia schizophrenia is an illness characterized by delusions hallucinations odd behavior and is among the top 10 leading causes of disability in the United States affecting approximately 1% of the general population can cannabis cause it nearly 2,000 studies have been published on this topic over the last half century and we hear about the pro psychotic effects but how clear is that link well population studies have consistently demonstrated a strong dose dependent association between cannabis use and the risk of psychotic disorders this is what they mean by a dose response studies showing that the more cannabis people used the more likely they were to be psychotic but that doesn’t mean cannabis is the cause it could just be a correlation or even a consequence of the disease yeah the link between cannabis and psychosis is well-established but maybe that’s just because patients with mental health problems self-medicate with cannabis to relieve their distress but there isn’t just a link between cannabis and psychosis in snapshot in time cross-sectional studies but in cohort studies as well where people are fault over time and so you can see the cannabis use often precedes the psychosis and not the other way around now it goes without saying that the vast majority of people who use cannabis do not develop schizophrenia and many schizophrenics have never used cannabis but overall these studies are considered to be strong enough evidence to warrant a public health warning there is another potential explanation though cannabis use proceed schizophrenia may be whatever genes drive schizophrenia also just make more likely you start smoking pot the biggest strike against the cannabis schizophrenia link or contact by country ecological studies that don’t seem to show more disease in areas where there’s more use and overall schizophrenia rates seem to have remained stable or even gone down worldwide since the sixties even though there’s been a big bump in cannabis use since then I mean if 10% of about 10% of schizophrenia cases are attributable to marijuana use and there’s been a four-fold increase in use why hasn’t there been a 40% increase in the prevalence of schizophrenia the problem with that argument is that there’s apparently little reliable evidence on the true trends in the incidence of schizophrenia or maybe it’s more of a potency issue rather than just cannabis in general the bottom line is you just don’t know when to you put it to the test you can’t just randomize kids to cannabis but in a way mother nature set up a natural experiment for us there are genes that kids randomly get that can increase their likelihood of smoking pot do those kids then go on to have a higher risk of schizophrenia yes supporting all those population studies as to just cannabis plays a cause-and-effect role in the development of schizophrenia okay but by how much let’s break it down even if cannabis use doubles risk that would only mean going from like a seven and a thousand chance of going crazy to like 14 mm so like a 140 chance to one and seventy chance now if it runs in your family that’s different and that doubling could mean going from like one in ten to one and five but on a population scale it could take you know thousands of users quitting to prevent a single case of schizophrenia so from a public health standpoint addiction is a far more common problem and people are probably not times more likely become addicted to marijuana even though that itself is relatively rare than to develop psychosis in their lifetime [Music] you