Marijuana Impairs Teens’ Working Memory

Significant numbers of American teenagers use/abuse the plant-based drug cannabis (especially marijuana); in addition, a smaller number of teens use/abuse an opioid drug or medication. In a study published in August 2014 in the journal Substance Abuse, researchers from four U.S. institutions explored the impact that cannabis use and opioid use have on teenagers’ ability to use a form of memory called working memory. All humans rely on this form of memory to record short-term information, focus attention and complete a range of essential tasks.

Teen Cannabis Use

The National Institute on Drug Abuse and the University of Michigan use a project called Monitoring the Future to analyze trends in substance abuse among the nation’s 8th, 10th and 12th graders. The latest available results from this project cover the year 2013. In that year, 36.4 percent of all 12th graders used/abused cannabis (marijuana or hashish) at least once over the course of 12 months. At least one yearly incidence of cannabis abuse occurred in 29.8 percent of 10th graders and 12.7 percent of 8th graders. In 2013, 22.7 percent of all 12th graders abused cannabis one or more times in the average month. Monthly cannabis intake rates for 10th and 8th graders were 18 percent and 7 percent, respectively. Cannabis abuse occurred on a daily basis among 6.5 percent of 12th graders, 4 percent of 10th graders and 1.1 percent of 8th graders. The rates for monthly and daily use/abuse in all three grades came within 1 percentage point of the rates recorded for 2012.

Teen Opioid Use

Monitoring the Future also analyzes trends in teen opioid intake. In 2013, 0.6 percent of 12th and 10th graders abused heroin at least once over the course of 12 months; 0.5 percent of all 8th graders had at least one yearly incidence of heroin use. Larger percentages of 12th, 10th and 8th graders abused the opioid medications OxyContin and Vicodin at least once in 2013; the peak rates for OxyContin and Vicodin use (5.3 percent and 3.6 percent, respectively) occurred among 12th graders. The monthly rate for heroin abuse in 12th, 10th and 8th graders was 0.3 percent. Monitoring the Future did not track monthly rates for OxyContin and Vicodin abuse in the three grades.

Working Memory

Working memory is the specific form of human memory that keeps track of events occurring in real time. As information comes in, working memory helps the brain keep that information “in mind” and use it to do such things as follow a conversation, follow instructions or complete mathematical or logical problems. Crucially, the brain relies on working memory as the underlying structure for a group of higher-level mental skills collectively known as executive function. Main examples of these skills, which only fully form in early adulthood, include the ability to make appropriate decisions, the ability to solve problems and the ability to control momentary impulses and pay attention.

Impact of Cannabis and Opioid Use

In the study published in Substance Abuse, researchers from the University of Maryland, Johns Hopkins University, the National Institutes of Health and Mountain Manor Treatment Center used data gathered from 42 teenagers receiving treatment for substance addiction to examine the impact that cannabis use and opioid use can have on teens’ working memory. Nineteen of these adolescents were mainly affected by cannabis addiction, while 23 percent were mainly affected by opioid addiction. Participants in both of these subgroups took two tests designed to measure their working memory skills.

After analyzing the test results, the researchers concluded that both opioid use and cannabis use substantially impaired the teenagers’ ability to properly use working memory. The larger deficits in working memory were found in the cannabis-using adolescents. This specific finding may at least partially reflect the fact that the mainly opioid-addicted teenagers enrolled in the study typically consumed just about as much cannabis as the mainly cannabis-addicted teenagers. The study’s authors believe that the heightened degrees of working memory impairment in the cannabis-addicted teenagers may also be partially linked to a generally lower socioeconomic standing among these individuals.

Broadly speaking, the authors believe that their work underscores the often-overlooked impact of diagnosable substance abuse/addiction on teens’ development of higher-level mental skills. In treatment, teens with serious working memory deficits may require different therapeutic approaches than their counterparts unaffected by such deficits.

Posted on October 5th, 2014

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