Residents of Missouri and Utah voted to legalize medical marijuana in yesterday’s midterm elections.

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Experts want to know the long-term impacts of using cannabis. Getty Images

Legalization of marijuana is moving forward in the United States and abroad, leading to increased access and important questions about its effect on teen users.

In yesterday’s elections, voters in Missouri and Utah approved legislation to allow medical marijuana use in those states. In Michigan, voters approved the legalization of recreational use of marijuana. These states join the dozens of other states that have approved marijuana either medically or recreationally.

As the drug becomes more common, more researchers are investigating whether or not the drug is capable of causing long-term cognitive impairments, particularly in those who start young.

New research published last month in the Journal of Clinical Psychiatry challenges the notion that marijuana’s effects on the adolescent brain necessarily turn into chronic cognitive problems.

“What we find is that adolescents and young adults who stop using cannabis improve in their ability to learn new information and those who continue to use don’t show that same improvement. We found that much of this improvement happens in the first week of abstinence,” Randi Schuster, PhD, the study’s lead author and assistant professor at Harvard Medical School, told Healthline.

The study is one of the first of its kind to use an experimental prospective model in which active adolescent marijuana users were compared with a group of their peers who were asked to abstain from marijuana use for 30 days.

Individuals in the abstaining group were asked to take urine tests to ensure that they were in fact not using marijuana.

The cohort consisted of 88 participants in total, ages 16 to 25. Both groups undertook a variety of different tasks to test two broad areas of cognitive functioning: memory and focus.

Researchers found that the group abstaining from marijuana had improved overall memory, but particularly verbal, the ability to memorize words. Attention did not improve with abstinence.

J. Cobb Scott, PhD, an assistant professor of psychology at the University of Pennsylvania School of Medicine told Healthline that the results were somewhat reminiscent of the conclusions of his own research.

Scott published a study earlier this year that concluded that individuals abstaining from marijuana use for more than 72 hours had insignificant cognitive impairment effects.

“The interesting thing is that it shows that a lot of the recovery takes place in terms of memory functioning in the first week [of abstinence]… I think this speaks a little bit to what we showed in our meta-analysis, which is that abstinence does have a pretty substantial effect on cognitive functioning in cannabis users,” Scott, who is unaffiliated with the first study mentioned, told Healthline.

Marijuana legalization groups have hailed the new study as more evidence that marijuana doesn’t lead to long-term cognitive impairment.

“These conclusions are consistent with those of prior studies finding that cannabis exposure isn’t likely to be associated with any sort of permanent adverse impact on the brain or cognitive performance following sustained abstinence,” Paul Armentano, deputy director of the National Organization for the Reform of Marijuana Laws, told Healthline.

“These findings dispute the long-standing ‘stoner-stupid’ stereotype and should help to assuage fears that cannabis’ acute effects on behavior may persist long after drug ingestion, or that they may pose greater potential risks to the developing brain,” he said.

However, experts have been quick to point out that the sword cuts both ways. An improvement in memory or cognitive functioning due to abstaining from marijuana means one thing: that there are in fact acute cognitive impairments caused by the drug in the first place.

“Does marijuana negatively impact a young person’s ability to think and process information efficiently? I think these data strongly support that notion because thinking ability gets better when they stop smoking,” said Schuster.

The American Academy of Pediatrics (AAP) also remains an outspoken opponent of marijuana legalization because of the potential access it could give to young users.

“We still have significant concerns about the impact of marijuana usage by teens — on their emotional and psychosocial development — and data still needs to confirm more about the possible effects on brain development and physical status,” Dr. Sheryl A. Ryan, chairperson for AAP’s Committee on Substance Use and Prevention, told Healthline earlier this year.

Areas of the brain, including the prefrontal cortex and hippocampus, are critical for cognitive functioning but also dense with cannabinoid receptors, which are targeted by tetrahydrocannabinol (THC), the primary psychoactive component of marijuana.

These areas of the brain are also least developed during adolescence — one of the main reasons that researchers believe that teen brains are more vulnerable to the negative effects of cannabis, said Schuster.

Both Scott and Schuster say that their work is essential to making sure everyone understands the risks and potential benefits of marijuana use. Schuster says that her next round of research will look at an even longer period of abstaining, six months, to see if cognitive functions continue to improve.

Her next study will also include those who don’t use marijuana, to test whether the cognitive improvement observed is really a “full return to baseline” — that is, whether abstaining from marijuana for an extended period of time will improve memory and cognition back to the level of an average teenager who doesn’t use marijuana.

“That will help us understand whether the amount of improvement that we saw in this study represents a full reversal of the cognitive deficits secondary to cannabis or if there is still a meaningful difference between marijuana users and non-users,” she said.

A new study finds that if teens abstain from cannabis use for just one month, their memory can improve.

Marijuana supporters say this points to the low risk of cannabis use. But some medical professionals point out that the improvement shows that cannabis use in general can negatively affect the brain.