Cannabis users performed better than those who never tried cannabis in a recent study that tested participants’ working memory.

“Although some suggest cannabis use during adolescence may have long-term consequences on brain development, the supporting science is ambiguous, with some studies suggesting negative outcomes and others suggesting no effect at all,” explained study author Brenden Tervo-Clemmens of the University of Pittsburgh.

Some research has found that cannabis use is associated with impairments in working memory — which stores and processes information relevant to the task at hand — but other research suggests the drug does little harm.

For their new study, the researchers recruited participants from the Maternal Health Practices and Child Development Study, a longitudinal study of the effects of prenatal drug exposure on children. The participants have been tracked since birth and were 28-years-old at the time of the current study. Fifteen of the participants had never used cannabis, 14 had tried cannabis but did not continued to use it, and 46 were repeated cannabis users.

The researchers used fMRI scans to observe the brain activity of the participants while they completed a test of spatial working memory ability.

“We performed neuroimaging on adults who had their substance use measured throughout adolescence,” Tervo-Clemmens told PsyPost. “We found that the age at which participants’ reported starting to use cannabis was associated with slower performance during a working memory task and that these behavioral differences appeared to be driven by regions of the brain associated with visual attention.”

In particular, the researchers found reduced activity in the right posterior parietal cortex among those who used cannabis earlier.

“However, the associations of age of cannabis initiation with working memory and brain function were not sensitive to the amount of reported cannabis use,” Tervo-Clemmens explained. “Moreover, compared to those who had never tried cannabis, cannabis users either performed better or did not differ on the working memory task.”

“Accordingly, the neurocognitive associations of age of cannabis initiation do not seem to be an outcome of cannabis exposure, but may instead be predictors of substance use initiation. That is, some adolescents may have an increased drive to experiment with drugs early that is predicted by working memory and brain function.”

The findings were published online in the scientific journal NeuroImage in December 2017.

But more studies need to be conducted before the researchers can make any strong conclusions.

“While we suggest brain function and cognitive performance associated with early cannabis use may be related to characteristics of the individual that precede cannabis use, here we only measured the brain after subjects had started using cannabis,” Tervo-Clemmens noted. “Studies measuring adolescents prior-to and following their initiation of cannabis use are essential for understanding whether adolescent cannabis use is associated with poorer neurocognitive function.”

“This field of research has clear public health significance, but the supporting literature is varied. Furthermore, cause-and effect relationships (as demonstrated in our study) are still uncertain.”

The study, “Adolescent cannabis use and brain systems supporting adult working memory encoding, maintenance, and retrieval“, was co-authored by Daniel Simmonds, Finnegan J. Calabro, Nancy L. Day, Gale A. Richardson, and Beatriz Luna.