Cannabis Legalization Encourages Neuroscience Research

With the recent changes in legislation regarding marijuana use in the United States, it is reasonable to conduct studies regarding exposure to warn potential users about its possible harm. A new study finds that people who have smoked cannabis as teenagers (16-18 years) performed 18% worse on long-term memory tests when compared to adults who have never smoked cannabis. People who have smoked marijuana for recreational use through the years could recall one-two words less from a memorized list of words. Although these results may have been subject to various confounding factors, such as alcohol and other drugs use, it is necessary to perform controlled studies to provide significant insight to marijuana use to the masses.

In a study published in JAMA Internal Medicine, a research team studied data from 3,300 people who took part in the long term Coronary Artery Risk Development in Young Adults (CARDIA). The sample consisted of 18-30 year olds who were followed during a 25 year period. Participants were asked about their marijuana use over eight points in time. Majority had said they have smoked marijuana at some point in life, yet most were simply occasional users who had quit when they reached middle age. About 11% remained active and heavy smokers. At the end of the 25 year study, participants were given a set of cognitive performance tests which demanded a recall of word lists to examine verbal memory, processing speed, and executive function. There was a statistically significant difference found in the area of verbal memory: those who had smoked consistently over a five year length of time displayed a slightly reduced ability in word recall on a list of 15 memorized words. Although these findings are not huge, record-breaking results, it provides a beginning link to recreational cannabis use to its effect on short-term memory.

A more conclusive study which links marijuana use to psychosis, schizophrenia, and structural changes in the brain was conducted by a Northwestern team at the Feinberg School of Medicine. Brain abnormalities and memory issues were observed in participants in their early 20's, two years after stopping their cannabis use. This study demonstrated how the hippocampus in the brain is shaped differently among heavy marijuana smokers, and this effect is related to poor long-term memory performance. As previous studies have showed poor short-term memory and working memory based on the abnormal shape of structures in the brain, it pinpoints brain regions which are critical for memory. The effects of poor memory on these individuals are shown to last for a few years after the stopping of its use. The longer a person heavily uses marijuana, the more abnormal the shape of their hippocampus. The study also found that adults with schizophrenia who heavily used cannabis as teenagers, performed 26% worse  on memory tests than adults with schizophrenia who have never used cannabis. 

In the United States, marijuana is the most commonly used drug among young adults, and the percentage is growing with the upcoming legalization laws. More studies need to be done in order to definitively show marijuana's impact on the brain, among other substances such as alcohol. Matthew J. Smith of Northwestern has said that it is possible that abnormal brain structures reveal a pre-existing vulnerability to marijuana abuse, and factors such as these are worthwhile to take into consideration in upcoming scientific studies.

References

Hippocampus. 2015 September ; 25(9): 1042–1051. doi:10.1002/hipo.22427.

John, Tara. "Marijuana Use Over Years May Affect Ability to Remember Words." Time. Time, 2 Feb. 2016. Web. 11 Dec. 2016.

Walton, Alice G. "Does Marijuana Affect Memory Over Time? Study Suggests So." Forbes. Forbes Magazine, 2 Feb. 2016. Web. 11 Dec. 2016.

Gavin, Kara. "Long-term Marijuana Use Associated with Worse Verbal Memory in Middle Age." Long-term Marijuana Use Associated with Worse Verbal Memory in Middle Age | University of Michigan Health System. N.p., 1 Feb. 2016. Web. 11 Dec. 2016.