I agree with you about psychotropic medications having a negative effect on people's driving and it is a problem. However, as a person who just retired after 25 years working for a fire department in a large town in Washington State... my impression is that in the last few years the number of stoned drivers causing serious “accidents” has been going way up. They are not difficult for us to spot after the fact. Increased marijuana use is already becoming a traffic safety issue... It is interesting that most pot users don't believe that it affects their own driving in a negative way. People who drink and drive generally feel the same way but with marijuana users it seems to be a much more strongly held belief.
My wife and I have a couple of older close friends who use a lot of marijuana for "medicinal purposes". The two of them have wrecked their Prius five times in the last year. The lady's sister told my wife that if they have one more accident that their insurance will be cancelled. They came up to our house a few days ago, he wanted to drive down to Costco while our wives visited. He scared the hell out of me in the Costco parking lot by driving too fast, nearly hitting a couple of other cars and almost running over a Costco employee pushing grocery carts. As we talked and I observed him I realized that he was probably high and it was most likely affecting his judgment.
I just hope that they lose their insurance and their licenses before they seriously injure or kill someone.