Some Actual Facts on Marijuana Effects

Here's one to file away where you know you can find it: Information on the difference between driving under the influence of alcohol vs. marijuana. By the unassailable Maggie Koerth-Baker, no less.

Some researchers say that limited resources are better applied to continuing to reduce drunken driving. Stoned driving, they say, is simply less dangerous.

Still, it is clear that marijuana use causes deficits that affect driving ability, Dr. [Marilyn A.] Huestis said. [Huestis is a senior investigator at the National Institute on Drug Abuse.] She noted that several researchers, working independently of one another, have come up with the same estimate: a twofold increase in the risk of an accident if there is any measurable amount of THC in the bloodstream.

The estimate is based on review papers that considered the results of many individual studies. The results were often contradictory — some of the papers showed no increase in risk, or even a decrease — but the twofold estimate is widely accepted.

The estimate is low, however, compared with the dangers of drunken driving. A recent study of federal crash data found that 20-year-old drivers with a blood-alcohol content of 0.08 percent — the legal limit for driving — had an almost 20-fold increase in the risk of a fatal accident compared with sober drivers. For older adults, up to age 34, the increase was ninefold.

The study’s lead author, Eduardo Romano, a senior research scientist at the Pacific Institute for Research and Evaluation, said that once he adjusted for demographics and the presence of alcohol, marijuana did not statistically increase the risk of a crash.... [emphasis added]

The difference in risk between marijuana and alcohol can probably be explained by two things, Dr. Huestis and Dr. Romano both say. First, stoned drivers drive differently from drunken ones, and they have different deficits. Drunken drivers tend to drive faster than normal and to overestimate their skills, studies have shown; the opposite is true for stoned drivers. 

It's pretty clear which drug is the real problem.