High-Dose Marijuana Exposure Among Teens Linked to Neurological Problems: Study

Humans and rats who saw high-dose THC exposure engaged in more risky behavior and decreased learning.

Using marijuana as a teen, especially at high doses, may increase the risk of impaired cognition, impulsive decision-making and other neurological problems, according to the findings of a new study.

Researchers used data from both human and rat studies to determine the long-term effects of marijuana on the brain, finding that high-dose THC use during adolescence was linked to reduced learning and impulse control. The findings were published on November 23, 2022, in the journal JAMA Psychiatry.

Researchers from the Icahn School of Medicine at Mount Sinai, New York, New York, used data from both a translational rat study and a reanalysis of a previously published dataset of human chronic cannabis users. The study included 37 participants who were chronic tetrahydrocannabinol (THC) users.

Decision-making was measured by the Iowa Gambling Task and Rat Gambling Task and impulse control was assessed in the rat model. Researchers focused on reward and punishment learning rates and learning strategies used by cannabis users and THC-exposed rats. They also conducted cell-specific molecular measures in the prefrontal cortex and amygdala areas of the brain to determine long-term effects.

Teen Marijuana Use Linked to Risky Behavior

Overall, the data indicated long-term THC use during the teen years was linked with risky decision-making and impulsivity in adulthood. Chronic cannabis users also scored lower on decision-making compared to control participants who were not marijuana users.

The data found long-term users favored exploration habits instead of long-term patience and gains. Meaning they were more primed for immediate results compared to waiting for long-term results.

Risky choice was linked with increased reward learning. This is when humans experience something unexpected, but the reward is not what we predicted. If the reward is greater, which is often the case in the brain when people use cannabis, it signals dopamine. If the reward is less, dopamine signaling decreases.

Essentially, this means THC users were met with increased dopamine levels for using marijuana, which increased their likelihood of using marijuana and the likelihood of doing risky behaviors that would also increase dopamine levels. This in turn led to reduced decision-making behaviors. They were less able to make difficult decisions and often took unnecessary risks as adults because of their marijuana use as teens.

This effect was seen among high-dose THC users but not low-dose THC users during their teen years.

Rats were also more likely to suffer cognitive impairments in adulthood after increased exposure to THC during adolescence. The results were similar to those seen in human users.

“In this translational study, high-dose adolescent THC exposure was associated with cognitive vulnerability in adulthood, especially with THC re-exposure,” researchers concluded. “These data also suggest a link between astrocytes and cognition that altogether provides important insights regarding the neurobiological genesis of risky cannabis use that may help promote prevention and treatment efforts.”