Marijuana Changes the Brain—and Not for the Better

Posted on January 29th, 2015
Posted in Marijuana

Like any other intoxicating chemical, the active ingredient in marijuana (THC) can affect biological functioning in a complex and multi-varied way. In fact, a new study on the effects of marijuana on the brain published in the Proceedings of the National Academy of Sciences finds that long-term marijuana smokers suffer a noticeable reduction in brain grey matter. In short, marijuana changes the brain, and not for the better.

The research team, headed up by Dr. Francesca Filbey from the School of Behavioral and Brain Sciences at the University of Texas at Dallas, recruited 48 dedicated pot aficionados, all of whom had begun their marijuana consumption between the ages of 14 and 30, to participate in their study. They also selected a second group of 62 non-consumers with a similar demographic profile for the purposes of comparison. They took great care in choosing candidates of mixed gender from varying age categories and backgrounds to avoid any biases that might creep into the study if its participants didn’t reflect the diversity of the pot-consuming community. Steps were taken to adjust for participants’ alcohol, tobacco and other drug use as well, so that any neurological changes observed could be tied directly to marijuana use.

Brain scans revealed that in contrast to the control group, long-term regular marijuana smokers had suffered a noticeable reduction in grey matter, specifically in an area known as the orbitofrontal cortex. This region of the brain is involved in decision-making, the generation of motivation and behavioral adaption in response to anticipated rewards or hardships. The orbitofrontal cortex helps us manage the problems and situations we face in our daily lives, and a lack of grey matter in this area forces the brain to make adjustments to prevent important mental functioning from being hopelessly compromised.

What was most revealing is that the younger a person started smoking marijuana, the more pronounced was their loss of grey matter. Some of the younger pot smokers in the study did show increased connectivity between various parts of the brain, and since this type of neurological intertwining is associated with adaptive/associative learning in general, this increase was likely a response to a loss of adaptability in the orbitofrontal cortex region. But examinations of older smokers revealed that after six or seven years of regular cannabis use, this extra connectivity begins to wither away, and if marijuana use is continued into later life, the brain’s ability to adjust to it becomes markedly reduced.

And of course no one knows exactly what abilities might be lost when the brain is forced to make such radical adaptations. In addition to brain scans, the study participants were given IQ tests, and the long-term marijuana users registered five points lower on these exams on average. This is not a huge drop-off, but when the development of young brains is tampered with, troubling results are to be expected, regardless of any neurological adjustments that might take place. An earlier New Zealand study recorded an average of eight points lost on IQ tests for long-term pot smokers.

News Flash: Marijuana Is Not Safe for Teens

It should be noted that the types of brain changes observed in heavy pot users are not found in those who began their habits at later ages. Because research suggests that the human brain does not finish developing until a person reaches their mid-20s, Dr. Filbey recommends that people hold off on marijuana experimentation until they reach at least this age range, when the risk of measureable neurological disruption is minimal.

But it is adolescents who appear to be particularly vulnerable to THC’s potent biological effects. As Dr. Filbey points out, “Adolescence is when the brain starts maturing and making itself more adult-like, so any exposure to toxic substances can set the course for how your brain ends up.” Of course, marijuana advocates will object to the characterization of their favorite drug as “toxic,” but from the standpoint of the still-forming young brain, that is exactly what it may be.

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