Alcohol exits the body in a matter of hours. Cocaine can take a couple of days.
Cannabis has no exact timetable.
The cannabis compound detectable in urine samples is evidence of past use, not actual impairment, said Dr. Alan Shackelford, a Harvard Medical School-trained physician who founded Amarimed of Colorado, a clinic in Denver focusing on medical marijuana. He has used cannabis to treat several children with rare seizure disorders who don’t respond to other medication.
The body metabolizes marijuana differently than most other substances, Shackelford said. Those who smoke or ingest marijuana feel a high for a short time from a psychoactive chemical in cannabis called THC, but its metabolites can remain in urine samples for weeks.
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There are many THC and other cannabis-related chemicals, but the two Shackelford notes are delta 9 THC, which causes the high, and carboxy THC, a metabolite that does not impair the user and remains in the body long after the high is gone.
“Here’s the thing that’s problematic. Blood or urine tests don’t look at delta 9 THC,” he said.
Drug testing companies, including Quest Diagnostics, use urine tests that seek evidence of past marijuana use — carboxy THC.
Five years ago, Shackelford sent a letter to the working group in Colorado that was considering rules that would allow police to judge driver impairment by using marijuana metabolite levels in blood or urine.
“You can’t do that. Cannabis is different (than alcohol),” he said in early September.
Because carboxy THC is fat soluble, it remains in the body longer than other substances, such as alcohol or opioid painkillers, which are water soluble. The time it lingers varies by individual, Shackelford said.
Factors that affect detectable levels include how often a person uses marijuana, how much body fat the person has, whether the person smokes or digests a cannabis product, and the concentration of the product itself, he said.
If someone who does not normally partake in pot chooses to smoke or eat a cannabis product on a Saturday and takes a urine test on a Monday, they might not test positive for carboxy THC, Shackelford said.
“If they do show positive … they are probably not impaired and are perfectly capable of doing any task,” Shackelford said.
But medical marijuana patients often use cannabis daily, Shackelford said. Daily users can test positive for weeks after their last dose. Medical patients have asked Shackelford what to do if they have to pass a drug test.
Shackelford tells them that products claiming to remove THC from the body don’t work. A few patients have reported back that stopping for 10 days helped them pass a drug test. Shackelford cautions it’s not a scientific study — few studies have been conducted in the United States because of federal restrictions.
TRACKING THE NUMBERS
In 1988, more than 13 percent of those who took drug tests with a company later acquired by Quest Diagnostics, called SmithKline Beecham Clinical Laboratories, tested positive for some illicit substance. Those rates have dropped since then.
However, from 2011 to 2015, more people tested positive for marijuana than any other drug, the data from Quest show. Positive marijuana test results also rose, from 1.6 percent of those tested to 1.9 percent in 2014 and 2015.
In 2014, of those who took a drug screen administered by Quest in Pierce County, 3.29 percent tested positive for marijuana. In King County, 2.71 percent checked by Quest tested positive for cannabis.
Statewide, 2.75 percent of those who took its drug tests were positive for marijuana.
The company did not provide the number of people who took the drug tests despite repeated requests, only the percentages of positive test results.
The company does collect samples in Thurston County, however not enough drug tests were conducted there to release data about those who took the tests, said Barry Sample, senior director of science and technology for Quest Diagnostics.
In recent years, the company has received a few requests to remove marijuana from its drug-screen panel, Sample said.
“Generally when they do the reason why they tell us, (is) they are having some difficulty finding employees that can pass the drug test,” Sample said. “They make the business decision.”
Since fewer people are applying for available jobs in this economy, people who fail drug tests are now more noticeable, said Sytease Geib, vice president of workforce development with the Thurston County Chamber of Commerce.
Drug testing policies, and the way drug tests screen applicants, are putting “reliable and eligible workers” out of work or preventing them from entering the workforce, Geib said.
“Although it’s legal, there are not sophisticated drug screens that can determine between ‘under the influence’ at work and (whether one consumes marijuana) recreationally on the weekend,” Geib said. “There is a desire to have something more scientific.”
Many companies, particularly those with federal contracts, still see a need for pre-employment drug screening.
“The safety and integrity of our operations, products and services is paramount,” said Boeing spokesman Chris Carter in an emailed statement.
Boeing, as a federal contractor, follows federal law in its rules for employees. Boeing workers are banned from using marijuana, regardless of the reason, said Carter.
Employees are tested before they are hired, after accidents, on reasonable suspicion and sometimes randomly as required by federal laws, Carter said.
Other employers may be adhering to zero tolerance policies for ideological reasons.
“For (companies) who have a policy prohibiting drug use … they assume that someone who uses marijuana has character traits that they want to screen out,” said Seattle attorney Aaron Rocke, who represents small employers and marijuana businesses. “If you are unemployed and fail a pre-employment drug screening test, you are behaving like the stereotype.”
Without federal changes, employer policies on drug testing are unlikely to change, said Sam Mendez, executive director of the University of Washington’s Cannabis Law and Policy Project.
“You would need to see some reform of the Controlled Substances Act,” Mendez said.
The act identifies illegal drugs, painkillers and hallucinogens regulated by the federal government. Marijuana, along with heroin and peyote, are on the Schedule I list: drugs that have a high potential for abuse and also have no medical use, according to the Drug Enforcement Administration.
In fact, on Monday the 9th U.S. Circuit Court of Appeals upheld a restriction on medical marijuana use for a California man, now on probation, who was convicted in federal district court of a drug-related offense.
Alan Nixon was prohibited from using controlled substances and required to comply with periodic testing.
About a year into his three-year probation term, he asked the court to modify his probation to allow medical marijuana use to comply with California’s Compassionate Use Act, which permits Californians to use medical cannabis for a variety of ailments.
The lower court “did not abuse its discretion by refusing to modify the conditions of Nixon’s probation to allow him to possess and use marijuana for medical purposes in violation of federal law,” the court ruled.
Mendez said if cannabis were moved to the Schedule II list — drugs that have a high potential for abuse but also have medical uses — then employer policies and other sweeping changes could happen around the country. Drugs on the Schedule II list include cocaine, methamphetamine and fentanyl.
“Then it becomes possible to be prescribed as medicine,” Mendez said of marijuana. “Then you would probably stop seeing people being fired for (testing positive) on a drug test.”
For another path, the feds could keep also keep marijuana on Schedule I, but exempt it in states with a legal and regulated marijuana market, Mendez said.
“It keeps the status quo (for the federal government) but it allows for greater movement in the different states,” Mendez said.
But could companies still test employees?
Mendez said marijuana becoming legal federally “doesn’t automatically make drug tests illegal.”