Marijuana-Use and the Young Brain

By Sandra Samuels, MD

Currently 20+ states are legalizing marijuana for medical and/or recreational use, and this trend is certain to continue for the near future. Therefore, it is of great importance for everyone to understand the risks; the brain is our greatest asset, and its damage is irreversible.

Neuroscientists are studying the brain from childhood to adulthood. Although, at age 10, the brain has achieved its adult size, the internal connections of the brain have not achieved maturity until 21 -22 years. Within this time, studies show that the neurons are making critical connections which affect memory and performance.

Developmentally, teens and young adults are switching from making decisions based on impulses from nuclei deep in the brain (amygdala) to the frontal lobes, where logic and planning rule decisions in adults. Therefore, though younger students may act or make decisions more quickly, they are less organized in the thinking process, and more likely to be impulsive and make mistakes. This has been shown repeatedly in experimental tests.

Support is found also in magnetic resonance spectrometry of the brain, which measures chemicals necessary for brain function. GABA (gamma-aminobutyric-acid) is an important chemical which controls negative feedback to the brain, allowing the person to suppress an incorrect response or action. This chemical is low in teenagers, and increases in adulthood.

Marijuana plays havoc with brain chemistry by lowering GABA, limits formation of important connections between the amygdala and frontal regions and prevents normal development of the teen brain.

Functional MRIs among marijuana users show deterioration of important brain structures – the corpus callosum, the amygdala, and connectivity of these to the frontal area of the brain. The frontal brain controls our executive decisionmaking functions and memory.

Studies have shown IQ changes from 99.7 to 93.9 in marijuana dependent users (daily or weekly, for 3 or more years) . IQ deterioration is seen after 1 and 2 years, to a lesser degree. In never-used persons, the average IQ remains stable or increases from 99.8 to 100.6

Due to judgment and perception problems related to marijuana, motor vehicle accidents have increased in Colorado, since it became legal for recreational use.

Habitual Marijuana use doubles the risk of serious psychotic disorders such as schizophrenia and suicide. This has been shown by many large studies around the world.

How does Marijuana differ from Cigarettes?

Thus, whereas the risks of cigarettes are well-known to include heart disease, cancer, stroke, emphysema and chronic bronchitis, the risks of marijuana are just recently being elucidated by scientific research. There is reason to believe that smoking marijuana, because of the many toxins in the plants, will result in complications similar to cigarette smoking.

Each of us needs to be well-informed of these risks, and should carefully determine their own marijuana risk, and decide whether to use or abstain.