Latest JAMA Studies Largely Fail To Support Past Claims About Marijuana And

Each research and the editorial have been revealed in the present day (Aug. 26) within the journal JAMA Psychiatry.

But the researchers found that brain volumes did not differ significantly between twins or siblings, even if one had used cannabis and the other had not, Agrawal said.

Experts agree that much remains unknown and the new findings just “scratch the surface”.

They found that over the four years, those who had smoked pot and also had several genes that increased their risk of schizophrenia had thinning in the cortex – the outer, gray matter of the brain – compared with those who had the same genes but had not smoked pot.

Study participants who’d used pot had on average, a slightly smaller amygdala and a slightly smaller right ventral striatum (another brain region, associated with the reward system).

“We do not know almost enough about effects of cannabis on the brain, especially the developing brain”, said Dr David Goldman of the National Institute on Alcohol Abuse and Alcoholism in Rockville, Maryland, in email to Reuters Health. Similarly, today’s JAMA study “casts considerable doubt on hypotheses that cannabis use … causes reductions in amygdala volumes”. Both the exposed and unexposed siblings in pairs discordant for cannabis exposure showed smaller amygdala volumes relative to concordant unexposed pairs. “When cannabis changes the brain, whether for good or more usually for bad, we need to learn whether the effects are pharmacologic in nature or due to shifts in socialization, study, work, exercise, or use of other psychoactive agents”.

This association was not observed among males with low risk or females with low or high risk for schizophrenia.

More than half the participants were male. Paus, a neuroscientist at the Rotman Research Institute, Baycrest in Toronto, and his colleagues used MRI to study the brains of more than 1,500 teenage boys. All were between the ages of 12 and 21 and in all of them, genetic testing had been done to assess their risk for schizophrenia. But this study did not test thinking ability or other actual clinical changes.

But in people who are genetically prone to schizophrenia, marijuana could alter their brain development in potentially negative ways, according to the other new study.

The authors used observations from three study samples and a total of 1,577 participants had information about cannabis use, imaging studies of the brain and a polygenic risk score for schizophrenia. Of course, there is definitely something to be said about appropriate use, so more studies will likely continue in the future. “If the illness runs in your family, discourage your kids from smoking pot when they are young”.

Professor Paus, a prominent researcher and pioneer in the field of population neuroscience, strongly cautioned that more research is needed to determine whether lower cortical thickness actually increases the probability of schizophrenia in at-risk men later in life. But we still don’t know everything about it. “All we are saying is that if you combine cannabis use with the genetic risk, then the brain is maturing in a slightly different way”, Paus told Live Science.

In the case of the amygdala, the researchers write that the smaller brain region may be explained by genetic factors – their analysis didn’t show a significant contribution from environment.

Goldman, who wrote an editorial accompanying the new studies, added in his email, “What this new research shows is that it is also unsafe to make assumptions about causality from correlation”.