Interestingly enough I did an experiment sponsored by the ARF back in the early 80s on the effects of marijuana on driving. I think there was up to 100 people in the study and it involved several visits to the old airbase at Downsview where they would take your blood and make you sit around for 4 hours each visit. First visit just baseline and they had us hit lights on a board kind of like a whack-a-mole and drive a course in their little Ford that was all wired up with sensors and like an Apple II in the backseat, pure 80s technology. The course was about a 5 minute drive and had several turns and a stop sign and then a gate-contraption, two lanes wide that would swing down from the top of the frame and randomly block one of the lanes. There was a tripwire about 20 yards away and you had to react doing at least 40 km. Interestingly enough they offered a bonus of $10 for every 10 km/h you exceeded that and successfully navigated the gate ( I think the whole study paid $200). The night of the test a few weeks later they made us smoke these little toothpick half-long joints stuck in a glass tube, then wait a half hour to take the blood again then out on the road. I used to drive an old plymouth fury that had once been a cab, and it was huge, and I noticed if you watched the gate at the top you could quickly tell which side was going to fall. AND back then the days that I hadn't driven high you could count on one hand (like smoking in movies back in the last century, lots of people did it, listen to War's Low Rider-- we even had an anthem. So that night I hit the gas in that little Ford and got it up to 80 km/h, and as the girl in the back screamed, I slalomed through that gage like the Transporter. Then they added a little twist, they threw a dummy on the ground before the last curve, it was clearly visible in the headlights from a good distance away, and I asked what the hell is that, and after repeating myself, the guy in the front awkwardly said just respond as if this was a regular drive. Anyhow, we had to stay the night for liability issues. Next morning the lady in charge of the study told me to keep an eye open for the final report being made public as they had found some interesting results and she implied she was concerned that her study results might not see the light of day. A year later I got a phone call and I was one of a dozen people they wanted to repeat the study for an NFB documentary, but sadly I had just entered grad school in a profession with more than a modicum of public exposure and respect so I had to pass. Never heard tell of either the study or the documentary since then. Long (long) story short, those MADD commercials with the guy stoned in the drive-thru forgetting why he was there is more than a bit of a reefer madness level exageration. But as per Useful's post, shrooms and edibles are a whole different story, as is driving drunk. Thank you for your civic mindedness, more people should care about each other.