You’re probably right, but let’s say you’re high and totally fine, a kid runs into the road and you hit them, how do you defend to the world that this was a tragedy that couldn’t be avoided and not due to impairment? I don’t think you could convince a jury of that, so even if right, you’d be screwed.

But I feel like there should be the obvious study of cannabis users at different levels of THC, and different tolerance histories on a standard obstacle coarse with response times measured when high vs not. I’m shocked that such a study isn’t readily available. That would be the gold standard (within group and within subject, plus dose response).

I did a quick search and found a bunch of “driving simulations” like this which shows that more THC resulted in worse driving and higher speed — which to me says the “I actually drive slower” argument doesn’t work.

But when you look at the actual effect sizes in the studies, they may be statistically significant but practically they’re only tens to hundreds of ms delay in reaction, so it’s hard to get a clear picture. Is 1/30th a second enough to prevent an issue? Over a million people and a million kilometres of driving, it probably adds up, but on an individual level you’d almost never be able to attribute an accident to this. I know my own reaction time to visual stimulus is like 150-300ms when we measured it for a physics lab project years ago (no idea if we did a good job or not), so like 5-10% of that seems fine.

tl;dr I’ve basically argued both ways, I tried doing a fact check and it’s messy, and I’m a little disappointed that the ethics teams can’t figure how to actually study this correctly.