Suppose you smoke a joint. Now, suppose you’re abruptly scheduled for a test upon which your career depends.
When is it appropriate to panic?
Scientists are still struggling to pin down the metabolic timetables for THC, the compound in cannabis that most actively promotes a high.
Unlike alcohol, THC’s presence in the bloodstream is not a consistently good indicator for intoxication, Vermont Health Commissioner Mark Levine tells us, because about 75 percent percent of it is gone after a half hour — well before a high has diminished.
About 90 percent of THC in the bloodstream vanishes after an hour and a half of smoking, vaping or ingesting pot, he adds.
Meanwhile, the “clinical” effects of the drug — potential impairment — “persist for up to four hours after smoking and 12 hours after ingesting THC,” Levine wrote in an email.
Traces of the drug linger considerably longer in body fat and in the brain, and are excreted gradually through bodily waste.
Half of the THC in a user’s body is generally eliminated this way within 36 hours, Levine said.
This exit pace, known as a “half-life,” continues for every subsequent 36 hours after a one-time toking or eating session.
“Elimination half-life is longer in regular cannabis users,” Levine added.
“So overall,” he writes, “while a blood test could be negative after 24 hours, urine testing after one-time use can be positive for a month, and among long term/heavier users (not referring to weight), test results can be positive for a minimum of a week, possibly up to three months.”
Researchers have yet to fully understand how and where THC behaves in the body, Levine concludes: “the concept of ‘traceable amounts’ is a complex one.”
