Alcohol consumption is associated with volume loss in the brain globally; even modest alcohol abuse may be associated with morphological changes and may represent an important confounding variable in studies on the effects of cannabis. – 2005, “Lack of Hippocampal Volume Change in Long-term heavy cannabis users”
There have been countless news items lately about how legalization of recreational cannabis in Canada must be a regime that keeps cannabis out of the hands of adolescents because cannabis, apparently, causes brain harms and, as one journalist put it, “a permanent reduction in intelligence and severe mental health problems later in life.” (John Roe, The Hamilton Spectator; 15 May 2017).
So, as a favour, I provide some research findings for all of you out there that point quite to the contrary. Addiction in teens: A survey of 216,000 adolescents from all 50 states indicates that the number of teens with marijuana-related problems is declining. Similarly, the rates of MJ use by young people are falling despite the fact that that more US states are decriminalizing or legalizing MJ (Grucza, R.A., et al., 2016; Martins et al., 2016; Choo, E.K., et al., 2014).
Further, in terms of your speculation that cannabis use in teens leads to long-term damage to the brain: Preliminary evidence shows that THC exacerbates, whereas CBD protects from, such harmful effects (see Lorenzetti; Hermann, D. & Schneider, M., 2012). Increasing CBD counts could reduce some of the harmful effects of cannabis, without compromising the effects users seek (The Lancet, Mar.1, 2017). “Daily use of MJ is not associated with brain morphometric measures in adolescents or adults,” Weiland, B.J. et al. 2015, Journal of Neuroscience 35(4),pp.1505-1512: There is no association between MJ use and standard volumetric or shape measurements of subcortical structures…
Other studies have found equivocal results (Lisdahl et al., 2014; Lorenzetti et al., 2014). MJ use has been associated with both increased (Cousijn et al., 2012) and decreased (Yucel et al., 2008) volumes of such structures, but these studies were not designed to determine causality, which would require a longitudinal design to establish temporal precedence. The problem is that most teens who take part in these studies, even the Waterloo study, have early age of onset use of alcohol, which causes volumetric loss in brain structures [the so-called “permanent reduction in intelligence” as you so unscientifically put it], and they don’t tell researchers about their alcohol abuse. Researchers then go looking for reasons for the brain harms that turn up on MRIs, and having no other culprit to blame, blame the cannabis.
“There were no differences between nonusers and daily users in the specific regions of interest [nucleus accumbens, amygdala, hippocampus, and the cerebellum–areas high in cannabis receptors]. We found no evidence of differences in volumes b/t daily users and nonusers, adults or adolescents; alcohol consumption is associated with volume loss in the brain globally; even modest alcohol abuse may be associated with morphological changes and may represent an important confounding variable in studies on the effects of cannabis. And, “Cannabis use is not associated with structural changes within the brain as a whole or the hippocampus in particular” (Tzilos, G.K. et al., 2005, “Lack of Hippocampal Volume Change in Long-term heavy cannabis users” in American Journal of Addiction #14, pp.64-72).
For an astounding study, see 1994’s Pediatrics peer-reviewed paper by Melanie Dreher et al., which conducted rigorous, longitudinal studies on 30 cannabis-ingesting mothers [and 30 control subjects who had no contact with the MJ] during pregnancy and on into breast-feeding, used to quell morning sickness, lessen labour pains and speed up the birthing process by facilitating uterine contractions. The cannabis moms and their kids did not appear to be harmed by marijuana exposure in the womb; there were no physical abnormalities, no cognitive, and no neonatal complications; nor were there any discernible disparities between the three-day-old babies of mothers who used marijuana and the three-day-old non-exposed babies. After one month the marijuana babies were actually healthier, more alert, and less fussy than the control group babies. Heavily-exposed babies were more socially responsive and more autonomically stable than babies not exposed to cannabis through their mother’s milk: “alertness was higher, motor and autonomic systems more robust, they were less irritable, less likely to demonstrate imbalance of tone, needed less examiner facilitation than neonates of non-using mothers.
When all the children were retested at ages four and five, Dreher’s team found “absolutely no difference” between the children of ganja moms and the children of non-users.”*
But I get it, time and space are of the essence when preparing journalistic work. And, further, it seems the media is enthusiastic in picking up the Gov’t refrain that MJ causes brain damage in teens. But the proof isn’t forthcoming on this matter, and people should understand that when hype appears in news articles in the form of cannabis causing “a permanent reduction in intelligence and severe mental health problems later in life,” they should have a little cautionary truth in their media feed to cut the horse-swill, don’t you think?
*Melanie C. Dreher, Kevin Nugent, and Rebekah Hudgins, “Prenatal Marijuana Exposure and Neonatal Outcomes in Jamaica: An Ethnographic Study, “Pediatrics 93(2) (1994):25-60.