When is a driver stoned? Pot groups fight over levels

Mar 26, 2012

An initiative to allow for personal marijuana use in Washington State will be on the ballot this November. And, while that initiative is getting support from many lawmakers – and even the Seattle bar association – pro-marijuana groups are battling over how much THC impairs a driver.

Initiative 502 would allow Washington residents age 21 and over to possess an ounce of marijuana for their own personal use.

A 25-percent excise tax would be established on pot sales, and laws prohibiting driving under the influence would be amended to include maximum thresholds for blood concentration of THC, the psychoactive ingredient in marijuana.

Setting the limit

I-502 proponent Allison Holcomb, of the group New Approach Washington, cites a study conducted by National Institutes of Health and the Harvard medical school of 25 long-term marijuana users that indicated a specific THC concentration of five nanograms per milliliter of blood as a guideline for separating impaired from unimpaired drivers:

“The average smoker will have their THC level drop below 5 nanograms per milliliter in 2 to 3 hours. THC does its spike and it drops down, it’s pretty consistent across the board regardless of the amount you are smoking,” Holcomb said.

Other research that looked at the THC levels of people involved in accidents was used to draw up the 5 nanogram limit, Holcomb added.

THC levels debated

But the idea of a specific criterion for determining when a person on pot is too impaired to drive is under fire from others in the marijuana community.

Douglass Hiatt is an attorney with the group Sensible Washington which sponsored another marijuana legalization initiative that failed to get enough signatures to qualify for the ballot.

Hiatt takes issue with the five nanogram limit:

“It’s set way to low,” he said, “and will create a huge number of DUIs.”

At least one member of the medical community agrees with Hiatts concerns. Dr. Gil Mobley is an emergency trauma physician who works in Washington state doing disability determinations and medical marijuana evaluations.

Mobley says his concerns over the five-nanogram threshold led to him to evaluate eight medical marijuana patients for their THC levels, combined with a series of neurocognitive and sobriety testing:

“Most of the patients that medicated twice a day never had levels that fell below 10 nanograms. After medicating, some patients would skyrocket to 60,70,80 and have completely normal neurological testing. They could pass a sobriety test. One lady, before medicating was in the teens, after medicating it was 147, that’s nearly 30 times over the five-nanaogram cutoff, and I’m telling you, this lady was fine to drive.”

Mobely thinks if I -502 passes, none of the medical marijuana patients in the state, estimated to be at least 25 thousand people, would ever be able to legally drive a motor vehicle in the state.

Attorney Douglass Hiatt also has concerns about drivers under the age of 21 who test positive for pot , regardless of the level  of THC in their bloodstream. He says under the conditions of I-502, such an infraction would lead to a DUI, without any proof of impairment.