Youth Brains Recover After Quitting Marijuana

Marijuana, it seems, is not a performance-enhancing drug. That is, at least, not among young people, and not when the activity is learning.

A study published recently in the Journal of Clinical Psychiatry finds that when adolescents stop using marijuana — even for just one week — their verbal learning and memory tends to improve rather quickly. The study contributes to growing evidence that marijuana use in adolescents is associated with reduced neurocognitive functioning.

Since the legalization of marijuana, there has been a trend of young people believing that marijuana poses less of a risk to their physical and mental wellbeing than other drugs or alcohol. However, studies tend to find that any substance use for youth is dangerous, especially for their developing brains. Researchers are particularly concerned with marijuana use among the young because THC, the active ingredient in marijuana, most sharply affects the parts of the brain that develop during adolescence, and with the mentality that marijuana is “natural,” the rising THC contents tend to be ignored.

“The adolescent brain is undergoing significant neurodevelopment well into the 20s, and the regions that are last to develop are those regions that are most populated by cannabis receptors and are also very critical to cognitive functioning,” says Randi Schuster. Schuster is the director of neuropsychology at Massachusetts General Hospital’s Center for Addiction Medicine and the study’s lead author.

Schuster and the team of researchers set out to determine if cognitive functions that are potentially harmed by marijuana use in adolescents — particularly attention and memory — improve when they abstain from marijuana.

They recruited 88 pot-using teens and young adults, ages 16 to 25, and got some of them to agree to stop smoking (or otherwise consuming) marijuana for the month.

Schuster says the researchers wanted to recruit a range of participants, not just heavy users, or those in a treatment program, for example. Some of the young people smoked once per week; some smoked nearly daily.

The researchers urine-tested both groups on a weekly basis to make sure that the THC levels for the abstinent group were going down, and that the levels for the control group were staying consistent as they continued using.

The researchers found that after four weeks, there was no noticeable difference in attention scores between the marijuana users and the nonusers. But the memory scores of the nonusers improved, whereas the users’ memories mostly stayed the same.

The verbal memory test challenged participants to learn and recall new words, which “lets us look both at their ability to learn information the first time the words were presented, as well as the number of words that they’re able to retrieve from long-term memory storage after a delay,” Schuster says.

Verbal memory is particularly relevant for adolescents and young adults when they’re in the classroom, Schuster says.

“For an adolescent sitting in their history class learning new facts for the first time, we’re suspecting that active cannabis users might have a difficult time putting that new information into their long-term memory,” Schuster says.

While this study didn’t prove that abstaining from cannabis improves adolescents’ attention, other studies have found that marijuana users fare worse in attention tests than nonusers. Schuster hypothesizes it might take more than four weeks of abstinence for attention levels to improve.

Interestingly, most of the memory improvement for the abstinent group happened during the first week of the study, which leaves the researchers feeling hopeful.

“We were pleasantly surprised to see that at least some of the deficits that we think may be caused by cannabis appear to be reversible, and at least some of them are quickly reversible, which is good news,” Schuster says.

In the meantime, Lisdahl says the findings from the new study — that abstinence from marijuana is associated with improvements in adolescents’ learning and memory — sends a positive message.

“I remain optimistic that we can show recovery of function with sustained abstinence,” she says.