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NIDA

NIDA Science Spotlight- Cannabis Effects on Driving Performance

Transcript

Dr. Marilyn Huestis Speaking:

We've wanted to study the effects of cannabis on driving.

We approached the Office of Drug Control Policy or ONDCP, to help fund this important project considering especially what is going on in our country now changing rules on cannabis.

NHTSA, the National Highway Traffic Safety Administration had built this incredible technology to study the effects of drugs on driving.

And NHTSA and ONDCP, worked with NIDA to conduct the very first ever study of an illicit drug in the National Advanced Driving Simulator.

This is a very important collaboration to look at the effects of cannabis with and without alcohol on driving and we hope that this can educate the public these effects.

So one of our first findings is the effect of cannabis on standard deviation of lateral position or weaving within the lane,

and we've shown that cannabis increases that weaving in the lane and that alcohol also increases that movement within the lane and when you put them together,

which is the most common co-occurence of drugs and drivers, you see that the additive affect of both of those drugs on driving performance and that's a public health and safety issue.

Also, because we had measurements of the cannabis before and after the drive,

all the time after they smoked we also have the alcohol measurements we were able to develop a model, that would tell us what the concentration of THC-delta-9-tetrahydrocannabinol, that's the main psychoactive ingredient in cannabis,

what concentration of THC, would equate with certain important levels of alcohol. Like .08 percent, which is the legal limit in the United States and we found that 13.1 micrograms per liter of THC produces the same affects on the SDLP, as .08 percent of alcohol.

Another very critical factor though, is these are the measurements of THC in the blood at the time of driving and unfortunately it takes a number of hours, usually somewhere 2 to 4 hours after a policeman stops someone for impaired driving,

or perhaps after the accident before we get the blood and THC decreases very rapidly so the amount during the drive of between 8.2 and 13.1 micrograms per liter by the time you collect the sample, can be much lower maybe around one or two micrograms per liter.

This page was last updated June 2015