well accomplishments like making music, coming up with ideas, having good conversations, putting together some good food combinations, playing better at video games, and just enjoying things more are plausible, but things like going out and building a house, or having ambition to go out and find a job stoned doesn't happen. maybe they are placebo and they say it to feel better about themselves.
People who say things like "OMG The Beatles smoked pot and look at what they accomplished!" are deluding themselves. The Beatles would have gone down in history with or without drugs. The drugs just happened to be "the thing" at the time, and it took them down certain musical paths.
And they never actually recorded music while high. The only ones who did that were the Grateful Dead, and they sucked.