The below article reports on the correlation between marijuana use and psychotic illness with a special focus on schizophrenia. See also the NIDA for more information on what is known about the use of marijuana. Much of this information we will cover inclass later this week and next. Click here for more information on this issue and other information on marijuana from the NIDA web site.
Researchers say they have the strongest evidence yet that using cannabis increases the risk of later developing psychotic illnesses such as schizophrenia.
On average, cannabis smokers have a 41% greater chance of suffering from such disorders than those who didn't inhale, the new study finds. And the likelihood increases with increasing cannabis use, with heavy users - who smoke daily - three times as likely as non-users to develop psychotic illnesses.
Cannabis is the most commonly used illegal drug in the world. In the UK and the US, for example, around 40% of young adults have used cannabis, according to government research.
Previous research has suggested a link between cannabis and schizophrenia-like symptoms such as paranoia, hearing voices and seeing things that are not there. But the possible association "has been an issue of tremendous debate and controversy for a long time", says Rick Rawson, a professor at the University of California in Los Angeles, US. "The science gets all mixed together with all the ideological views [about the drug]."
Now, researchers in the UK have reviewed 35 studies on the long-term effects of cannabis use in Europe, the US and Australasia and say the drug does in fact appear to be linked with an increased risk of psychosis. The original studies lasted from one to 27 years.
Causal link? Because people with pre-existing mental health problems may be more likely to take drugs in the first place, the researchers excluded data from those already showing signs of psychotic illness. Still, they found an increased incidence of psychosis in cannabis users, suggesting the drug may somehow cause such disorders, they say.
"Although you cannot be certain that the cannabis is causing this increase in risk, we think there is enough evidence to warn people," team member Glyn Lewis of the University of Bristol in the UK told New Scientist.
If cannabis does cause psychosis, it could account for at least one in every seven cases of diagnosed psychotic illness, the researchers say.
"There is a very good reason to be concerned," says Shaul Hestrin of Stanford University in California, US, who is investigating how cannabinoids affect brain cells. He says the evidence of a causal link in this latest study is "very convincing" but adds that even better evidence may come once scientists understand how cannabis actually changes the brain.
Rawson agrees: "The big question is how to determine who's at risk."
The British government is now reviewing the classification of cannabis, which is currently a Class C drug. It may be reclassified as Class B, which means users could begin to do jail time for possession.
"Clearly the health risks are only some of the factors that are taken into account when people consider the legal classification of drugs," Lewis says. This latest study was funded by the UK Department of Health, and Lewis said the results have been given to the UK Home Office.
Journal reference: The Lancet (vol 370, p 319).
