Frequent use of cannabis boosts the risk of depression and schizophrenia according to studies published in the November 23 issue of the British Medical Journal (BMJ).
More use – higher risk of depression and anxiety
A study in the southeastern Australian state of Victoria followed 1 601 school students, aged 15-15, for seven years, regularly checking their health and interviewing them about their
By the age of 20, 60 percent had used cannabis, and seven percent were daily users.
Among frequent users, young women were especially prone to reporting depression and anxiety, according to the researchers.
Those who used it daily were more than five times likelier to have these symptoms compared with non-users, whereas weekly users had a two-fold risk.
Picture not the other way around
"These findings contribute to evidence that frequent cannabis use may have a deleterious effect on mental health beyond a risk for psychotic symptoms," say the authors, led by George Patton, a professor in adolescent health at the Murdoch Children's Research
Institute in Parkville, Victoria.
Some opinion suggests that the picture may be the other way round - that people who are depressed smoke cannabis in order to make themselves feel happier.
But Patton's team says it found no evidence of this.
Teenagers who were depressed or anxious were not especially likelier to go on
to smoke cannabis.
Direct pharmacological effect
It speculates that, because the depression risk appears to be confined mainly to daily users, the answer lies in "a direct pharmacological effect."
Cannabis, they argue, affects receptors in specific brain cells that influence memory, emotions, cognition and movement. And the effects could be compounded by "psychosocial mechanisms – for example, the adoption of a counter-cultural lifestyle."
Higher risk of schizophrenia
A Swedish study, also published in the BMJ, found a dramatic incidence of schizophrenia among heavy users of cannabis.
Those who had smoked it more than 50 times were at least six times likelier to be diagnosed with schizophrenia, it found.
The research is based on more than 50 000 conscripts whose health and well-being were at first monitored in 1969-70, and which were routinely followed up until 1996.
The volunteers self-reported their use of cannabis and other drugs; any mental disorder was formally diagnosed by psychiatrists.
The findings are "consistent with a causal relation" between schizophrenia and intensive cannabis use, the study says.
"This association is not explained by sociability personality traits, or by use of amphetamines or other drugs." – (Sapa)