From The Epoch Times
As states ease up on marijuana possession laws, police, legislators, and a skittish driving public worry how this trend will impact road safety. Cannabis
clearly has an influence on driver performance, but there is a wide range of opinions about how long to wait after the last toke before getting behind the wheel.
With more states allowing medical and even recreational cannabis, the federal government has been encouraging safety precautions with tougher restrictions for DUI. To date 14 states have traded their effects-based standard to one that establishes a conviction based on blood test results. A driver impairment law that relies on the presence of a substance is called a per se law.
These per se laws essentially treat cannabis like alcohol, where a blood concentration threshold for tetrahydrocannabinol (THC)—marijuana’s psychoactive chemical—legally determines inebriation. Most states have a .08 blood alcohol per se law to determine if a person is drunk, and a zero tolerance policy for THC, where any amount is justification enough for a DUI conviction and a suspended license.
Just like with alcohol, drivers who test at or above this per se threshold are considered unfit to drive. The recent measure passed in Washington state sets the bar at the high end of the spectrum—five nanograms of THC per ml of blood.
At first glance the notion seems to make good sense—especially given the last 25 years of success with alcohol per se law enforcement in lessening traffic fatalities. However, experts say a THC blood test will never produce a similar result because of a fundamental difference in pharmacokinetics.
First, a cop with a Breathalyzer can accurately measure blood alcohol, but not THC. While authorities talk of an oral swab test in the works, right now THC requires a blood test, which by law must be administered by a licensed medical professional, who may not be available for several hours after the initial arrest.
The most important difference with alcohol is that blood THC has proven to be an unreliable measure for intoxication. Unlike alcohol, THC levels are highest upon first ingesting the drug, yet the greatest impairment does not come until about 20 minutes later after blood THC levels have plummeted. While marijuana smoke can leave a few nanograms of THC lingering in the system for 24 hours or more, research has shown that driving ability usually returns to normal in just a few hours.
The National Highway Traffic Safety Administration (NHTSA) says that time rather than THC level is a more accurate gauge for evaluating a safe or unsafe driver. Results from NHTSA’s comprehensive 1993 study (a government trial that put cannabis smokers behind the wheel in both a closed course and in heavy urban traffic) found that driver performance noticeably diminished the first two hours after smoking. Driving skills returned to baseline sobriety about three hours after inhalation, and sometimes even improved.
For those familiar with the prevailing science, strict THC per se laws have been a hard sell, but supporters argue that the science is changing. A study released in this month’s American Association of Clinical Chemistry looks at chronic marijuana users at a deeper level than before.
Lead author Marilyn Huestis, chief of chemistry and drug metabolism at the National Institute on Drug Abuse, is at the forefront of this new look at THC blood levels. Dr. Huestis has been studying the effects of marijuana for decades, and her latest report observes a trend demonstrated over three published papers.
While the majority of scientists say the effects of marijuana dissipate relatively quickly, Huestis reports that both THC and impaired performance linger in the brains of daily users for weeks after their last puff. The chronic users Huestis observed were still excreting THC from their tissues even after a month of abstinence, and did not respond as well as the control group in psychomotor and divided attention tasks.
According to Heustis’s conclusions, all regular cannabis consumers—including patients who have demonstrated a medical necessity—would automatically become a traffic risk in the eyes of the law even after weeks of abstinence.