Editor's note: This column has been updated to provide attribution to original sources.

Preliminary evidence from a new study led by Harvard Medical School Affiliate McLean Hospital's Staci Gruber, PhD, suggests that medical marijuana (MMJ) may not impair, and in many cases, may actually improve executive functioning in adults. Splendor in the Grass? A Pilot Study Assessing the Impact of Medical Marijuana on Executive Function, assessed the impact of MMJ treatment on executive function and explored whether patients improved cognitive functioning. "After three months of medical marijuana treatment, patients actually performed better, in terms of their ability to perform certain cognitive tasks, specifically those mediated by the frontal cortex," explained Gruber in a press statement.

Previous studies have shown that anxiety often interferes with both attention and executive function, so if MMJ products relieve anxiety, it is likely that a patient's cognitive function may improve. Chronic pain also impairs cognitive performance, especially in tasks requiring executive function, so a reduction in pain will likely increase concentration and cognitive performance.

"Symptom improvement may therefore result in improved cognitive performance," wrote the authors. "Interestingly, two previous studies have noted a positive association between a history of MJ use and improved cognitive performance on measures of psychomotor speed, attention, working memory, executive functioning, and verbal learning in patients with bipolar disorder compared to patients without a history of marijuana use."

The subjects in the study completed the Wechsler Abbreviated Scale of Intelligence, "which provides an estimate of overall cognitive functioning, to ensure an estimated IQ of 75 or higher," according to the study. Each participant also completed several executive functioning tasks, such as the Stroop Color Word Test, the Trail Making Test, and the Wisconsin Card Sorting Test. After three months of MMJ treatment, participants completed tasks significantly faster, without making any more errors.

The study also suggested that MMJ products themselves may protect against the executive function deficits that affect most recreational marijuana users because of the inherent differences between MMJ and recreational MJ products. MMJ products are often--but not always--low in THC, the primary psychoactive constituent of the plant, and high in other cannabinoids, including CBD, a non-psychoactive component touted for its therapeutic potential, which may also mitigate some of the negative effects of THC.