Marijuana and driving: How much is too much?

Two U.S. states, Colorado and Washington, have recently legalized the recreational use of Marijuana and both are struggling with the question of how much is too much when it comes to Marijuana and driving.  Colorado and Washington have both recently passed legal limits for tetrahydrocannabinol or THC in the blood at 5 ng/ml but Washington’s is a “per se” law while Colorado’s is not.  A per se law sets an intoxication standard based purely on the concentration in the blood.  So in Colorado, even if a driver is above the 5 ng/ml limit they have the opportunity to present evidence that they are not impaired.

Some marijuana advocates argue that the 5 ng/ml standard is too low and that some medical marijuana users are always above that level.  What is the right level?

Below is a very unscientific examination of the issue by a local television station in Washington State.

http://www.kirotv.com/videos/news/stoned-drivers-hit-test-course/vqPqJ/

There doesn’t appear to be a scientific consensus on what the maximum THC blood level should be.  The National Highway Traffic Safety Administration in the U.S. is researching the issue with results expected next year.  Until more research becomes available the debate continues.