 Is cannabis-impaired driving a public health and safety concern? Well, the number of tickets went up for cannabis-impaired driving in Washington state after legalization, and the proportion of drivers in fatal car crashes in Colorado who tested positive went up. But in both cases, this may simply reflect the general increase in marijuana use overall. It doesn't mean that cannabis is causing the crashes. Yeah, there's lots of evidence correlating marijuana use with car accidents, but you have to ask yourself, who uses marijuana, mostly young people and males, and guess who has higher crash risk regardless of what they smoke? Young people and males. But taking that into account, it does seem that roughly 20 to 30% of traffic crashes involving cannabis use occur because of the cannabis use. To put that in perspective, though, that number is more like 85% when it comes to alcohol. Yeah, but are the cannabis crashes just like low-velocity fender-bender bumps from some wasted driver going like five miles an hour? After a systematic review of the literature, this compilation of studies examining acute cannabis consumption and motor vehicle collisions found a near doubling of risk of a driver being involved in a motor vehicle collision resulting in serious injury or death. So that's pretty serious, though, again, alcohol is even worse. Yes, cannabis may double or triple the risk of car crashes, but alcohol may multiply the risk like 6 to 15 full. The combo may be even worse, though, 25 times the odds of fatal car crash involvement, testing positive for both. The safety consequence of cannabis intoxication when driving is listed as a primary concern about cannabis legalization. OK, well what happened in the states where marijuana was legalized? How much did traffic fatalities go up? They didn't. In fact, they went down. What? Why does legalizing pot reduce traffic fatalities? Because it reduced alcohol consumption. They found that legalization of weed was associated with reduced alcohol consumption, so yes, more drug driving, but less drunk driving. And that's so much worse that overall fatalities went down. So perhaps we'd also see less liver disease, less alcohol-induced brain damage as pot substitutes for some of the alcohol use. Cannabis is unlikely to produce as much harm as alcohol because unlike alcohol, cannabis does not cause liver or gastrointestinal diseases, not fatal in overdoses, and does not appear as neurotoxic as alcohol, and it's not as potent a cause of car crashes as alcohol either. The health problems of cannabis dependence like bronchitis and memory impairment are much less serious on average than those suffering from alcohol dependence. But this does not mean that cannabis dependence is a minor problem, but public health authorities can be criticized for bringing that up. It's like in the 40s and 50s after the repeal of prohibition. You still need to warn people about the problems of heavy drinking and liver cirrhosis, alcoholism, but you just get dismissed as some temperance propagandist, and now we see a similar thing where the public health profession wants to educate people about the adverse health effects of cannabis, but are dismissed as reefer madness hysterics. Still, it's important to put these adverse health effects in perspective. How does the safety of cannabis stack up against alcohol and tobacco? Well according to the CDC, alcohol is linked to approximately 88,000 deaths per year, whereas the deaths that do to cannabis are from things like car accidents and they go down when more people smoke pot because alcohol is so much worse. With hindsight, we can clearly see the enormous problems that have been caused by the legal drugs, tobacco and alcohol. If asked to decide today which psychoactive drugs should be legal, cannabis might well be much higher on the list.