This study suggests that cannabis abstinence is associated with improvements in verbal learning that appear to occur largely in the first week following last use. Associations between adolescent cannabis use and poor neurocognitive functioning have been reported from cross-sectional studies that cannot determine causality. Prospective designs can assess whether extended cannabis abstinence has a beneficial effect on cognition.
https://www.ncbi.nlm.nih.gov/pubmed/30408351
