As of January 1, 2018, possession and recreational use of marijuana became legal in the state of California. The passing of Proposition 64 in 2016s general election, marked a shift in California’s position toward the substance still deemed a Schedule I drug by the U.S. Drug Enforcement Administration—the same category as ecstasy, LSD, and heroin. The new law went into effect on January 1st and includes measures for safe use around marijuana.
Among the safe use measures is the prohibition from driving under the influence of marijuana. This seems like a good idea to us! The consequences for driving under the influence of marijuana, and alcohol are the same under California’s new law. The problem, however, is detection; alcohol disappears from the user’s blood and brain as the effects wear off, while marijuana may remain detectable in a user’s blood for days—and sometimes weeks—after consumption.
Alcohol impairment is strongly linked with how much the user has consumed and is subject to the users height, weight, sex, and other factors, but alcohol will still show up in the users' blood. That is to say, one glass of wine no matter the affect, is subject to the standard blood-alcohol content limit. No such standard currently exists for marijuana though. THC—the psychoactive chemical in marijuana—can affect people differently, so measuring THC in the user has not proven a reliable. States that have…well…blazed a trail in the legalization of marijuana (namely Washington and Colorado) have nevertheless set a THC limit, while California did not and instead issued a directive within the law that drivers may not drive under the influence of any drug.
So, in California, a DUI conviction related to marijuana relies heavily on what officers on the scene can smell, see, or otherwise observe. Users may also be subject to blood or breath tests and less commonly, urine tests. Transportation reporter Eli Wirtschafter of NPR member station KALW reports that while there remains no uniform DUI test, several newer technologies developed in the Bay Area—inclusive of a veritable marijuana breathalyzer, as well as an app that can test a driver’s impairment—may be helpful in the pursuit of reliable testing.
Until they get it all sorted out, we at Car Talk urge our readers not to drive under the influence of anything that may potentially impair your judgment or driving ability; safety should always supercede legality.