Driving Under the Influence, of Marijuana

http://www.nytimes.com

If you are pulled over on suspicion of drunken driving, the police officer 
is likely to ask you to complete three tasks: Follow a pen with your eyes 
while the officer moves it back and forth; get out of the car and walk 
nine steps, heel to toe, turn on one foot and go back; and stand 
on one leg for 30 seconds.

Score well on all three of these Olympic events, and there’s a 
very good chance that you are not drunk. This so-called standard 
field sobriety test has been shown to catch 88 percent of drivers 
under the influence of alcohol.

But it is nowhere near as good at spotting a stoned driver.
In a 2012 study published in the journal Psychopharmacology, 

only 30 percent of people under the influence of THC, 
the active ingredient in marijuana, failed the field test. 
And its ability to identify a stoned driver seems to depend heavily 
on whether the driver is accustomed to being stoned.

A 21-year-old on his first bender and a hardened alcoholic will
 both wobble on one foot. 
But the same is not necessarily true of a driver who just smoked 
his first joint and the stoner who is high five days a week.
 In another study, 50 percent of the less frequent smokers 
failed the field test

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Tommy Chong and Cheech Marin in the film “Up in Smoke.” 

In one study, only 30 percent of drivers who had smoked marijuana 

failed a sobriety test. Everett Collection

As more states legalize medical and recreational marijuana, 

distinctions like these will grow more and more important. 

But science’s answers to crucial questions about driving 

while stoned — how dangerous it is, how to test for impairment, 

and how the risks compare to driving drunk 

— have been slow to reach the general public.

“Our goal is to put out the science and have it used for

evidence-based drug policy,” said Marilyn A. Huestis,

a senior investigator at the National Institute on Drug Abuse.
“But I think it’s a mishmash.”

A 2007 study found that 12 percent of the drivers
randomly stopped on American highways on Friday
and Saturday nights had been drinking.
(In return for taking part in the study, intoxicated drivers
were told they would not be arrested, just taken home.)..... [...] http://www.nytimes.com