Colorado drivers now need to learn new limits for Driving Under the Influence of Drugs (DUID). House Bill 1325, which sets limits on blood levels for driving after smoking marijuana, has been passed by the Colorado Senate and now awaits Governor John Hickenlooper’s signature. If signed by the governor, drivers whose blood exceeds five nanograms per millileter (ng/mL) of THC per milliliter will be presumed to be driving while stoned.
The bill allows drivers who have been charged with DUID to argue whether they were impaired at the five ng/mL level. This is unlike impairment of alcohol charges because the driver cannot argue whether the 0.08 blood alcohol level (B.A.C.) truly impairs the driver.
The legislature drafted the bill to allow the driver to refute the five ng/mL level because THC can linger in users for longer periods of time. Typically the ng/mL level of THC is extremely high upon initial use and drops off after two to six hours. Some studies have indicated that habitual users would not be affected by this law because habitual users can sustain a level of THC below five ng/mL days after use.
On the other hand, other studies have shown that users may still have ng/mL levels more than five days after use. Dr. Lantz, the head toxicologist from Rocky Mountain Labs, claims to have test results from an individual showing a 20 ng/mL level at 24 hours after last use. At this level, the legislature feels someone is too high to drive, but the legislature has recognized that it’s next to impossible to determine actual impairment via a blood test under currently available testing technology. Therefore, the legislature has written the bill in a manner that allows users to argue whether their ng/mL level amounted to actual impairment.