Lawmakers in Washington state, where recreational marijuana use is now legal, are trying to determine how police officers can identify drivers impaired by marijuana use, The Wall Street Journal reports. There is no consensus on what blood level of THC, the active ingredient in marijuana, impairs driving, the newspaper notes. Breathalyzers cannot be used for marijuana.
In Washington, drivers with five nanograms of THC per milliliter of blood are considered to be under the influence. Drivers arrested or convicted of driving under the influence for alcohol or drugs must install an ignition interlock device. The device is not effective for detecting marijuana.
In Colorado, where recreational marijuana use is also legal, legislators passed a measure earlier this month that also sets a five-nanogram legal limit on THC. That bill gives drivers a chance to prove they were not impaired.
R. Andrew Sewell, Assistant Professor of Psychiatry at Yale School of Medicine, says the link between THC levels and driving impairment is not clear. A person who has built up a tolerance to marijuana may not be impaired at the five-nanogram limit, he says. Sewell notes THC leaves the blood quickly. Setting these limits “is going to cause a lot of impaired drivers to be missed and it’s going to cause a lot of innocent people to get arrested,” he told the newspaper.
Less than 1 percent of the country’s police officers are fully trained in sobriety tests for drugged drivers, according to the International Association of Chiefs of Police.