From infancy to the age of 25, the human brain goes through a dramatic growth process that solidifies the essence of a person: likes, dislikes, temperament, senses of touch and smell are all determined within the first five years of a human life. Within the teenage years, a person’s judgement begins to form that is independent of their intellect and academic abilities, and will be fully-formed around the age of 25. Therefore, any substance or environmental factor that could inhibit this development is discouraged by doctors.
While cannabis seems to have little effect on adult brains over 25, doctors are concerned by cannabis use among teenagers, and want to warn them on the dangers of using cannabis before the brain is ready. “You should know what you’re getting into. You should know what will happen,” said Jennifer Golick from Muir Wood Adolescent and Family Services in Marin County, CA. “Be an informed consumer — you make the choice.” Golick sees about 180 children as patients who have cannabis dependency and understands drug abstinence education has little effect on the teenage population.
In terms of recreational substances, alcohol, heroin, cocaine, tobacco, ecstasy and methamphetamine are far more lethal than cannabis. In fact, lethal overdoses of cannabis are non-existent due to how cannabis is processed in the human body and the amount needed to trigger an overdose. But doctors want teenage patients to know that a non-lethal substance can still be harmful.
According to Sion Kim Harris, a researcher at the Center for Adolescent Substance Abuse Research at Boston Children’s Hospital, teenagers involved in heavy cannabis consumption often have decreased neurocognitive function and brain development. This is due to THC’s effect on neurons in the hippocampus, decreasing their activity in a part of the brain responsible for memory and learning. If the hippocampus has prolonged exposure to THC during the developmental phase, it could lead to undersized development and therefore decreased function. Since a human brain doesn’t fully develop until the age of 25 or so, teenage brains are more easily-influenced by internal and external stressors, and are more adept at learning and adapting to new influences. If neurons in the hippocampus are less active over time, the brain naturally disables these neurons, which affects memory formation.
“That is one of the biggest issues for teens — the ‘opportunity cost,” Harris said. “Learning is the number one job for teens, and if they are having problems with learning, that will impact their ability to grow into adulthood.”
Research has also shown how THC affects the growth of brain matter, and how electrical pathways in the brain can be weaker. Myelin, the substance responsible for insulating neurons and other nerve cells, does not form as well in the presence of chronic THC consumption. “So the implication is your brain is slower.” said Harris.
“There’s a problem with cognitive processing. It’s not as sharp or as strong. It’s harder to maintain focus.”
There is also a connection between how early the brain is exposed to harmful substances and the severity of developmental damage. According to one report,
“The brain does not complete development until approximately age 25, and data from the field of alcohol use reflect that substance use exposure during this period when the brain undergoes rapid transformation could have a more lasting impact on cognitive performance.”
Researchers at the academy admit that there’s no clear connection between cannabis and academic performance, due to the infinite number of variables that affect cognitive brain development, they do suggest “this interference in cognitive function during the adolescent and emerging adult years, which overlap with the critical period in which many youth and young adults’ primary responsibility is to be receiving their education, could very well interfere with these individuals’ ability to optimally perform in school and other educational settings.”
But in teenager’s whose family has a history of mental illness, marijuana use could lead to a higher likelihood of that illness presenting itself. “We are seeing these kids develop schizophrenia at a younger age than their parents or other family members developed it,” Harris said. “Marijuana use seems to be a precipitating factor.”
The consensus seems to be that cannabis is use is fine, but only after you’re finished growing. “I don’t care who uses, or how often, if you’re over age 30,” said Harris. “But we’re seeing these critical developmental issues in people up to their mid-20s.”