Two new studies published online recently in JAMA (Journal of the American Medical Association) Psychiatry provide little support for previous claims that cannabis exposure is significantly harmful to the developing brain.
The first study, which assessed the effects of cannabis exposure on brain volume in exposed and unexposed sibling pairs, reported that any identifiable differences “were attributable to common predispositional factors, genetic or environmental in origin.” By contrast, authors found “no evidence for the causal influence of cannabis exposure” on brain morphology.
The trial is “the largest study to date examining the association between cannabis exposure (ever versus never used) and brain volumes.”
The study is one of two recent clinical trials to be published in recent months rebutting the claims of a widely publicized 2014 paper which alleged that even casual marijuana exposure may be linked to brain abnormalities, particularly in the region of the brain known as the amygdala. In January, researchers writing in The Journal of Neuroscience reported “no statistically significant differences … between daily [marijuana] users and nonusers on [brain] volume or shape in the regions of interest” after researchers controlled for participants’ use of alcohol. Similarly, today’s JAMA study “casts considerable doubt on hypotheses that cannabis use … causes reductions in amygdala volumes.”
A second study appearing today in the journal assessed whether cannabis use during adolescence is associated with brain changes that may be linked to an increased risk of schizophrenia. While researchers reported finding an association among male subjects who possessed a high genetic predisposition toward schizophrenia, authors reported that no such association existed among male subjects who were at low risk for the disease, or among females in either the high risk or low risk categories. The finding is consistent with the theory that early onset cannabis use may potentially exacerbate symptoms in a minority of subjects predisposed to the disease, but it contradicts claims that marijuana exposure is a likely cause of schizophrenia, particularly among those who are not already vulnerable to the disease.
Abstracts of both new studies appear online in JAMA Psychiatry here and here.
This piece first appeared on the NORML Blog
State of Psychosis says
I don’t even believe that the increased risk among teens is true.
at least it wasn’t for me when i was younger. I had the exact opposite effect. quitting it was the worst decision i’ve ever made.
I am schizophrenic and if it wasn’t for weed i would be dead right now. guess what? my worst suicide attempt of my life happened after i quit weed for a year. When i was sitting in the bathtub bleeding out I said screw it and smoked a joint I stole off my roomate… it was only after that that I came to out of the blackout and stopped the bleeding. furthermore, after 10-15 years of using it, my schizophrenia has improved so much that it’s almost gone completely! I don’t even have auditory hallucinations anymore. this stuff is a miracle! I’m really sick of politicians trying to use us mentally ill people as a political football to justify laws that have done nothing but bully people like me.
speak out against it.
don’t let them use us anymore.
there are tons of people like me who use it to treat their schizophrenia and we’re all doing just fine.
Other studies have already been finding no link at all even in teen use.
Also, even if causation theory was true, it would just be another arugment to put a legal age limit on the stuff.
good luck convincing any politician ever