Study alleviates some fears that teen marijuana use causes long-lasting damage

A new study examining the effect of a marijuana-like substance on rats suggests the drug is not as harmful to memory as is sometimes believed.

“In our study, we show that mild marijuana use as a teen is not detrimental to working memory performance, so long as use does not persist into adulthood,” explained one of the study’s authors, Erin K. Kirschmann of the University of Pittsburgh.

She told PsyPost the research “alleviates some fears that any use dooms the individual to a life of cognitive impairments. However, cannabinoid use during adolescence did show evidence for addiction liability, so we are by no means promoting the use of cannabinoids for teens!”

The study, published in the peer-reviewed journal Neuropsychopharmacology, was the first to investigate a rodent model of adolescent cannabinoid self-administration. In previous research, experimenters have administered the primary psychoactive constituent of marijuana — tetrahydrocannabinol (THC) — to rats because rats are not particularly inclined to voluntarily consume the substance. However, Kirschmann and her colleagues found that rats will voluntarily consume a similar substance called WIN55,212-2 (WIN).

Both drugs have similar mechanisms of action in the brain. Like THC, the synthetic substance WIN is a cannabinoid receptor agonist.

“Our lab is interested in understanding the long-term consequences of adolescent exposure to stressors or drugs of abuse on cognition, impulsive behavior, and risk for neuropsychiatric disorders,” Kirschmann told PsyPost.

“Multiple neural systems are undergoing tremendous change during this time period, and factors like stress or drug use might shift normal developmental trajectories and impact cognition, stress-reactivity or substance use later in adulthood. I am particularly interested in understanding the implications of cannabinoid exposure (i.e., marijuana use) during adolescence. Because the legislation around marijuana use has become much more relaxed, it is important to gain a better idea of what teen marijuana use does to the brain.”

In a surprise to the researchers, they found that adolescent self-administration of WIN was associated with improved working memory performance in adulthood. They also failed to find evidence of long-lasting deficits in short-term memory. In other words, the researchers found rats did not suffer long-lasting memory impairments from consuming the synthetic cannabinoid in adolescence.

The researchers also found that self-administration of WIN resulted in some addiction-like behaviors in the rats. But the self-administration of WIN did not result in an escalation of intake, which is typical of addictive drugs.

“We are not promoting the use of marijuana in teens, but we are suggesting that original reports of major detriments in all cases of teen use may not be the full picture,” Kirschmann said. “We also have unpublished evidence to suggest that continued use in adulthood can produce cognitive impairments (so, again, we are not promoting the use of marijuana as a way to improve cognition).”

That research and more is on its way. Kirschmann said on caveat of the current study is that it only examined male rats.

“We have just repeated our experiments using female rats and have found similar results – mild cannabinoid exposure during adolescence followed by abstinence can either cause improvements or no change in working memory performance in adulthood,” she told PsyPost.

“We still need to address what neurobiological mechanisms are altered because of cannabinoid exposure alone, and in conjunction with cognitive changes. We know that the inhibitory signaling in the brain, particularly in the prefrontal cortex, is involved. We also want to see whether impaired cognitive performance is a risk factor for later marijuana use, or if the marijuana use causes the cognitive impairments (sort of the ‘chicken or the egg’ question).”

The study, “Effects of Adolescent Cannabinoid Self-Administration in Rats on Addiction-Related Behaviors and Working Memory“, was also co-authored by Michael W. Pollock, Vidhya Nagarajan and Mary M. Torregrossa.