Just How High? – The Difficulty of Drug Testing

The recent legalization of recreational marijuana in Colorado has proven to be an economic boon for the citizens of the state. From the $98 million in pot sales and excise taxes expected by the state government in the coming year to the $5 million collected by dispensaries in their first week of sales, the drug promises a lot of dollars for stakeholders in the industry. Even the young entrepreneurs of the Girl Scouts found profits in catering their cookies to hungry smokers (until an official pronouncement by the organization barring sales outside of weed stores).

A drug testing vial, courtesy of the American Civil Liberties Union.

For the average marijuana user, however, the threat of personal economic ruin due to employment drug testing may outweigh these societal benefits, even in states where recreational or medicinal use is legal. In one well-publicized example, a quadriplegic customer service representative for DISH Network, Brandon Coats, was laid off in 2010 after testing positive for the medical marijuana he consumed to manage his chronic pain. Although Coats lived and worked in Colorado, where the medical use of the drug was legal at the time, DISH lawyers successfully contended that the continued illegality of marijuana use under federal law meant that his consumption was unlawful.

Importantly, nearly all drug tests commissioned by employers, including the one that led to the firing of Coats, do not detect the presence of marijuana’s active ingredient, tetrahydrocannabinol (THC). This molecule, which causes the general changes in consciousness associated with the drug, is completely metabolized by the body within three to eight hours. Therefore, most tests detect the presence of non-psychoactive compounds formed by the breakdown of THC, which stay in the body far longer than the four to ten hour window of impairment from marijuana use.

Detection times vary widely based on a user’s past history with the drug and body type; metabolites such as THC carboxylic acid (THC-COOH) are fat-soluble and thus remain in the systems of people with more body fat for longer periods. Urine tests, the most common analysis method, can generally detect frequent use for 10 to 21 days after the drug was last ingested. Hair tests, however, can indicate previous marijuana intake for months after the last use.

Most legal entities fail to distinguish between the previous use detected using these tests and the current impairment that might be of danger to society. The detection of THC-COOH in urine samples from DUI cases, for example, is often used as evidence for the presence of THC in the bloodstream at the time of arrest. Yet this conclusion may be incorrect, as the test could be measuring drug use from weeks before the incident. Only six states (including Colorado) have established limits for actual THC in drivers, which is measured using a blood test.

As support for marijuana legalization continues to grow, it will be vital for law enforcement to establish methods for separating impairment from previous use. While no equivalent to the Breathalyzer exists for pot, police could seek the advice of workplace human resources managers, who are developing rapid cognitive tests to determine impairment. Such tests will strike a fairer balance between individual liberty and societal protection.


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