State Bill Would Create THC Limit for Stoned Drivers, but Scientists Say It's Useless

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Most cannabis activists, law enforcement professionals, and biologists agree that blood tests don't work very well to police stoned drivers. Unlike alcohol, which dissolves in blood, THC, the active chemical in marijuana, dissolves in fat, and doesn't "peak" in the body while you're actually high. In February, a Columbia University neurobiologist told NPR that it's "really difficult to document drugged driving in a relevant way."

Apparently, that news has not reached State Rep. David Silvers, a West Palm Beach Democrat who filed a state house bill yesterday to impose a legal blood-THC limit on Florida drivers.

Silvers' bill would amend the state's driving-under-the-influence statutes to stipulate that anyone with five nanograms or more of THC in his or her bloodstream while driving (or boating) would be guilty of driving under the influence of drugs.

Silvers, a first-term representative whose district includes portions of West Palm, Lake Worth, and Palm Springs, did not respond to a call from New Times. The bill's timing is obvious: Florida legalized medicinal cannabis in November, and lawmakers in cities and counties across the Sunshine State are now scrambling to decide how to regulate legalized weed.

But biologists, however, have long warned that blood tests aren't very reliable when it comes to pot smoking. Technically, when a person smokes weed, some THC is released into their bloodstream in the next few hours. But the drug's effects can linger on for more than a few hours, while THC levels in the bloodstream don't.

There are two huge problems to testing for the compound. For one, THC builds up in the bloodstreams of habitual marijuana users, which means those users could fail blood tests even if they aren't high.

Also, there are multiple ways to ingest marijuana, and only some of those ways lead to increased blood-THC levels. Edible marijuana, like pot brownies, typically doesn't lead to increased THC levels in the bloodstream, according to NPR.

Likewise, a 2016 study from the AAA Foundation for Traffic Safety called similar blood tests "useless" for deducing who's too stoned to drive. The study said that multiple states already impose the same, five-nanogram limits on drivers and that the rule is both impossible to police, and has no real effect on driver safety either. According to AAA, people with more than five nanograms of THC in their blood don't even drive much worse than regular drivers.

In 11 states, you can be arrested for having any THC in your bloodstream while driving: This means some people can be arrested for a DUI despite having not smoked for days or even weeks.

Currently, stoned Florida drivers can only be pulled over for driving erratically on the road.

One other, major group that says these bans are useless. The federal National Highway and Traffic Safety Organization says it's both "inadvisable" and "currently impossible" to track how stoned a person is via their blood-THC levels alone.


In a phone interview, Silvers said he had not reviewed studies on the efficacy of using a THC blood-test to test driver impairment before filing the bill.

"The bill can always be amended, and that's what makes this country so great," he said.

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