12/13/2010 11:44 am ET | Updated May 25, 2011

DUI Pot Bill Could Lead to Wrongful Convictions

With national polling showing that nearly one in every two Colorado voters supports ending marijuana prohibition, and an estimated 120,000 residents registered with the state as medical marijuana patients, the debate over pot promises to remain hot as we head into 2011. Next up on the media's radar: a legislative proposal to penalize those who drive while high. Great idea, but could faulty science lead to wrongful convictions?

As 9News' Adam Schrager reported Thursday, state Rep. Claire Levy, a Boulder Democrat, is championing a plan to treat those who get behind the wheel while under marijuana's influence similar to those who drive drunk.

Here's the problem. While existing scientific technology can, in most cases, accurately test whether a suspected drunk driver has a blood alcohol level at or above the .08 legal limit, attempts to apply a similar standard to those accused of driving under the influence of marijuana (equal to five nanograms of marijuana's main component, Tetrahydrocannabinol, according Levy's plan), do not provide an accurate assessment of a driver's intoxication.

When it comes to alcohol, evidence of consumption generally leaves a person's blood stream within eight hours, meaning that if it's in someone's system, chances are very good that consumption came within this time frame. But with marijuana, THC can stay in the human body for 30 days or longer. Also problematic, most jurisdictions do not employ testing that adequately distinguishes between "active" and "inactive" THC (the active ingredient in marijuana).

THC blood tests are also problematic given that two individuals of identical weight, height, and THC blood levels could demonstrate dramatically different levels of intoxication, a fact tied to differences in frequency of use, strain of marijuana consumed, as well as other biological or medical conditions.

Also at issue is human error. The Colorado Bureau of Investigation is currently reviewing several dozen blood tests that were used by Colorado Springs prosecutors to charge or convict DUI defendants. While these cases involved alcohol, they demonstrate, at minimum, the flaws that can come from even the most minor testing methods or equipment errors.

While Colorado Attorney General John Suthers told 9News that "virtually everybody at that (five nanogram) level would be impaired, unsafe to drive an automobile," national experts vehemently disagree.

According to the National Highway Traffic Safety Administration, "It is difficult to establish a relationship between a person's THC blood or plasma concentration and performance impairing effects."

The NHTSA also cautions that blood tests may not accurately reflect actual intoxication due to differing impacts tied to various methods of ingestion, most commonly in a smoked or vaporized form, or more recently, through THC-infused edible food products.

Blood tests don't also account for how frequency of use factors into a person's intoxication. Marijuana is like most other drugs, including everything from caffeine to cocaine, in the sense that a daily user can build up a tolerance to specific amounts, and thus function at a much different level than the once-a-week or once-a-year user.

Ultimately, the NHTSA concludes that "it is inadvisable to try and predict effects based on blood THC concentrations alone...It is possible for a person to be affected by marijuana use with concentrations of THC in their blood below the limit of detection of the method."

The devil will be in the details for Suthers and Levy. Suthers says he is motivated by the goal of helping give clarity under the law for all involved, ideally freeing up court dockets now too often clogged with a flurry of experts testifying as to many of the same NHTSA findings expressed above.

The legislature should proceed with caution. Absent essential protections for the accused, including a right to testing that would accurately distinguish between "active" and "inactive" THC in the blood, as well as the right to have blood retested at a reasonable cost by a certified lab, Colorado's courts could become even more clogged by those defendants wrongly accused and eager to take their cases to trial.

While the effort to deter drivers from getting behind the wheel while intoxicated is laudable, especially given the recent surge in medical marijuana patient registrations, the wrong bill here could do far more damage than good. As our nation's history has proven time and again, even the most solid of public policy goals can be derailed if faulty or inadequate science is allowed to serve as the foundation for determining guilt. Let's join together to deter and punish driving while high or drunk, and as part of this effort, reject science that won't also exonerate the innocent.

Jessica P. Corry ( is a Denver-based attorney, where she serves as special counsel to Hoban & Feola, LLC, and where her practice specialties including medical marijuana civil and criminal law.