HealthDay News  — Teenagers who smoke marijuana daily may have lingering memory problems and structural abnormalities in the brain, even after they stop using the drug, a small study suggests.

Researchers found that young adults who’d smoked pot heavily as teens performed worse on memory tests than their peers who’d never used the drug regularly. And on brain scans, they tended to show differences in the shape of the hippocampus — a brain structure involved in forming long-term memories.

However, the findings, reported in the journal Hippocampus, do not prove that marijuana is the culprit.

That’s partly because the study participants were assessed only once, which leaves the chicken-and-egg question open, said lead researcher Matthew Smith, an assistant professor of psychiatry and behavioral sciences at Northwestern University Feinberg School of Medicine, in Chicago.

This study, Smith said, adds another layer: It found a correlation between the oddly shaped hippocampus and memory problems.

What’s more, the young adults in this study had been marijuana-free for an average of two years. That suggests that if heavy use alters teenagers’ brain structure, or dims their memories, the effects do not quickly go away, Smith said.

More research is needed, he said, to see just how long those effects might last after young people stop smoking pot.


Smith MJ, et al. Cannabis-related episodic memory deficits and hippocampal morphological differences in healthy individuals and schizophrenia subjects. Hippocampus. 2015; doi: 10.1002/hipo.22427.