What's The News, Mary Jane?

Every now and then you read a headline and think that doesn't make any sense.  That's how I felt when I saw the widespread story "Fatal Car Crashes Involving Pot Use Have Tripled in U.S., Study Finds."  No matter how you feel about drug policy, the basic numbers seem odd.  Because, no matter what else, while there's been a recent uptick in marijuana use, it's come nowhere close to tripling.

Let's look at what the study actually says. It compares 1999 to 2010.  The numbers are compiled from six states--California, Hawaii, Illinois, New Hampshire, Rhode Island and West Virginia--that routinely perform toxicology tests in fatal crashes.  Drugged driving in general rose from 16% to 28% over the decade, but where marijuana was the main drug involved, it rose from 4% to 12%, the tripling in the headline.

Researchers, however, noted "severe limitations" to the research since many illegal drugs can be detected in the blood up to a week after use, so marijuana's appearance in a toxicology test doesn't necessarily measure intoxication of the driver.

In general, drug use in the U.S., including marijuana (which is more popular than all other illegal drugs combined), had been going down for years, bottoming out around 2007 or 2008, and recently going up again.  In fact, it's possible marijuana use had gone down slightly from 1999 to 2010, and if it did go up, it'd only be a few percentage points.

So even if there was a rise in use, a tripling in fatality still seems way too high.  What factors might account for this number?

First, perhaps further research will not show the same rise.  If someone said the number was up 50%, I'd think that on the high side, but reasonable.

Second, the numbers are still relatively small compared to alcohol-related death, which stayed steady at 40%.  When numbers are at the tail end, large fluctuations are more likely.

Third, some say the potency of marijuana has increased recently.  If that were true, then steady use would probably result in more accidents.  (There's also the question if users use it more, though I don't know of any evidence for that.)

Fourth, if the stigma of marijuana use is going down, it's possible users, especially newer ones, are more likely to make it a casual part of their lifestyle, and thus more likely to drive while intoxicated.

A fifth related point is the stigma attached to drunk driving.  For decades groups have been fighting against drinking and driving, but not nearly so much about smoking and driving.  In fact, with recent fights for legalization of marijuana, it's possible that stigma has become even less significant.

Which brings us to our final point: traffic fatalities have been going down a lot recently, perhaps due partly to the higher stigma of intoxicated driving. In 1999, 15.3 out of 100,000 Americans died in a motor vehicle fatality, but by 2010, it was down to 10.6, a huge drop. And most of that drop came in the latter half of the decade.  So if other causes were going down, while marijuana use was steady or rising, it would likely be a much bigger factor in deaths.

I still think the number is too high, but no matter what it is, it can't be said enough that--while we celebrate greater safety overall--driving under the influence of any drug is a bad idea.