A new meta-analysis of the results of four clinical trials of vaporized cannabis (VACs) finds strong evidence that VAC use may impair Cognitive Control. The study findings are published in JAMA Network Open.

The authors analyzed data from three randomized controlled studies conducted between 2009 and 2019. In the results of those studies participants taking VACs reported lower cognitive performance after 24 weeks than in patients who were not using VACs.

This was very surprising given that these studies were designed to assess fluctuations in cognitive function not actual performance. said lead author Dr. Yvette Babbitt associate director of the Stanford Center for Addiction Neuroplasticity (SANT) and an assistant professor of psychiatry UC San Francisco School of Medicine Los Angeles. But given the findings we suspect that a decline in cognitive function might be an accurate reflection of the more common use of VACs.

One of the studies included in the meta-analysis measured a specific measure of cognitive control (Waskom-Angan-Lit outcome modulo multiple-choice reaction time) and found a significant drop in Waskom-Ang score reduction (10 percentage points relative to placebo). Another study involved 56 adults aged 19 to 65 years who were randomized into one of four groups. In the low-VAC group participants reported significantly less powerful effects of affective effects on Waskom-Ang cognitive ability (93 46 percent in low VAC compared to 99 14 percent in placebo-treated control) and reported fewer changes in cognitive flexibility (88 41 percent versus 99 34 percent). There was no significant difference in affective effects cognitive flexibility or memory for participants in the VAC-only group (P. 05).