Purple haze, all in my brain… but just for the next three days.

Jimi Hendrix sang about the aftereffects of drugs in his 1967 song.

And, to this day, the effects of marijuana on brain development in teens and young adults remains a contentious topic.

Previous studies have linked teenage marijuana use with numerous developmental risks, including a decline in cognitive ability.

But a new study is challenging that.

Published this month in the journal JAMA Psychiatry, the study concludes that prior research “may have overstated the magnitude and persistence of cognitive deficits associated with use.”

Additionally, the researchers found that people who abstained from marijuana use for longer than 72 hours had insignificant cognitive issues after that time period.

“Our analyses suggest a detectable but limited association between cannabis use and cognitive functioning in adolescents and young adults; for a majority of individuals, such effects may be of questionable clinical significance, especially after sustained abstinence,” the authors write.

What the study uncovered

The meta-analysis looked at data from 69 studies published between 1973 and 2017.

In total, the studies included 2,152 individuals described as heavy or frequent cannabis users and 6,575 nonusers as a control group.

This month’s study is the first of its kind to perform a meta-analysis of research on the association between cognitive dysfunction and cannabis in teens and young adults, as opposed to just adults.

“By doing this analysis, we get to see more precise estimates of how big these effects are and how long they last, as opposed to individual studies, which have typically been small, but people have drawn lots of conclusions from them over the years,” J. Cobb Scott, PhD, assistant professor of psychology in the department of psychiatry at the University of Pennsylvania Perelman School of Medicine and the study’s lead author, told Healthline.

Pro-marijuana groups have been quick to seize on the study.

“These conclusions are consistent with those of prior studies — in particular, recent longitudinal twin studies reporting that cannabis use is not independently associated with any residual change in intelligence quotient or executive function,” said Paul Armentano, the deputy director of the National Organization for the Reform of Marijuana Laws.

“These findings 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 added.

Opposition remains strong

However, vocal critics of the risks posed by marijuana to teens and young adults remain.

The American Academy of Pediatrics (AAP) is staunchly opposed to legalization of marijuana for both recreational and medical use.

This new study has done little to change that position.

“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 of brain development and physical status,” Dr. Sheryl A. Ryan, chairperson for AAP’s Committee on Substance Use and Prevention, told Healthline.

Ryan notes that a major drawback of the study is that it didn’t include any longitudinal data as part of its analysis. So, it does little to help understand what the potential long-term effects of marijuana on cognitive functioning could be.

The study was limited to examining cognitive functioning, and Ryan said there are myriad other concerns for teens using marijuana, including lung health, risk of developing psychosis, and academic achievement.

“We need to know more about the long-term effects on our youth, in terms of many aspects of development, and until we know more from rigorous scientific studies, we still need to be cautious about minimizing the risks of marijuana use among our youth,” said Ryan.

Understanding the substance

According to Scott, the researchers’ intent wasn’t to downplay the risks of marijuana among teens, but to help create a more comprehensive understanding of it.

“We certainly aren’t encouraging use in teens or even young adults,” Scott said. “But our data point to the fact that [the effects] are certainly smaller than has been previously found.”

His approach, he said, is practical.

“The reason to study it in teens is because they are doing it. There’s not much we’re going to do that’s going to stop that. So, if they are going to use [marijuana], then we should have a real evidence-based understanding of what are potential risks of use, why they are using despite these risks,” he said.

Marijuana is also playing an increasingly larger role for the treatment of certain medical conditions.

This month, the U.S. Food and Drug Administration, for the first time, recommended approval for Epidiolex, a drug derived from cannabis that’s used to treat epilepsy.

With medical marijuana and cannabis-derived medication on the market, understanding how they’ll affect teens is of the utmost importance.

“There is a lot that we don’t know in this space. Just because something is illegal doesn’t mean we shouldn’t study it and understand its effects,” Scott said.