A recent study suggests that daily marijuana use in teens may have a small effect on memory problems and structural abnormalities in the brain.

Researchers found that young adults who smoked cannabis heavily as teens often performed worse on memory tests than young adults who had never used the drug regularly. Brain scans also showed some differences in the brain, specifically in the hippocampus- a part of the brain heavily responsible for memory.

Although these studies do show these findings, the tests were only conducted once and researchers can not link a casual relationship between marijuana and shortened memory. In other words, this study strictly proves a small correlation rather than a causation.

“We can’t know that it’s causing the memory impairment,” said Smith, an assistant professor of psychiatry and behavioral sciences at Northwestern University Feinberg School of Medicine, in Chicago.

Researchers are continuing to dive into the study of marijuana, especially with legalization booming across the United States. More research will soon provide many answers for the open debate on the safety of marijuana use.