Long-Term Pot Use Can Double Risk of Psychosis
Young people who smoke cannabis or marijuana for six years or more are twice as likely to have psychotic episodes, hallucinations or delusions than people who have never used the drug, scientists said on Monday.
The findings adds weight to previous research which linked psychosis with the drug — particularly in its most potent form as "skunk" — and will feed the debate about the level of controls over its use.
Despite laws against it, up to 190 million people around the world use cannabis, according to United Nations estimates, equating to about 4 percent of the adult population.
John McGrath of the Queensland Brain Institute in Australia studied more than 3,801 men and women born between 1981 and 1984 and followed them up after 21 years to ask about their cannabis use and assessed them for psychotic episodes. Around 18 percent reported using cannabis for three or fewer years, 16 percent for four to five years and 14 percent for six or more years. For most of the study, researchers didn't measure the frequency of cannabis use among subjects, but rather whether they used at all.
"Compared with those who had never used cannabis, young adults who had six or more years since first use of cannabis were twice as likely to develop a non-affective psychosis (such as schizophrenia)," McGrath wrote in a study published in the Archives of General Psychiatry journal.
. . .