It only been two years since marijuana legalization through out all of Canada. The old saying: stoners are slackers, DUMB, slow etc just to name a few.
With the legalization those stigmas really didn't make sense anymore. We still got those (old ways) thinking that every time you pull from a joint, you get a lower IQ.
A review made by Canadian researchers Scot Purdon and Daniel Kryzanowski deliberating on what are the long-term cognitive effects on a regular smoker. Their tests was mainly to study the impact of verbal learning and memory abilities. They study previous studies to back up their research.
The test concluded if going under abstinence for between 7 to 28 days the memory and verbal learning should resolve it self. Purdon didn't make only one research; he conducted a study that marijuana had the ability to hinders the verbal learning-ability to read and hold information - and that up to 24 hours after usage. After max 3 days, the effect is cut by half.