“This observational study examined the acute cognitive effects of cannabis.

We hypothesized that cognitive performance would be negatively affected by acute cannabis intoxication.

Contrary to expectations, performance on neuropsychological tests remained stable or even improved during the acute intoxication stage (THC; d: .49-.65, medium effect), and continued to increase during Recovery (d: .45-.77, medium-large effect).

Contrary to our hypothesis, there was no psychometric evidence for a decline in cognitive ability following THC intoxication.”

https://www.ncbi.nlm.nih.gov/pubmed/31790276

https://www.tandfonline.com/doi/abs/10.1080/23279095.2019.1681424?journalCode=hapn21