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How Long Can Weed Show Up in a Drug Test?

A study on some of the world's heaviest smokers may give us a better understanding of how long marijuana can be detected in urine samples.
Several nuggets of marijuana on display
J. Danielle Wehunt/Stocksy

Your friend arrives for his shift at the big-box home improvement store. He clocks in and his manager hands him a cup with a Quest Diagnostics logo on it. “Oh, fuck!” he thinks. As he makes a terrifying trek from plumbing to lighting to that weird aisle of doorknobs on his way to the men’s room, he frantically does some mental math. He stayed off the ganj last weekend, but the Friday before that, he had a few tokes at a bonfire. And last month, he got baked into red-eyed stupor binge-watching Rick and Morty. Are those bong hits out of his system yet? He is seriously considering offering a twenty to the stranger in that stall to fill the cup for him. Just how long does it take for cannabis traces to leave the body? Also, is there a more chill place in this strip mall that’s hiring? Like maybe Game Stop?


How does your body process marijuana?

The body cleans out the traces of cannabinoids through metabolism, and metabolic rates vary widely among individuals. “Each of us has a unique metabolism that processes cannabis at a different rate,” says Joseph Rosado, a medical consultant to International Cannabis Solutions, a Toronto-based consulting firm for governments, workplaces, and healthcare providers with marijuana-related concerns.

“Even among people of the same gender and age, individual lifestyle choices—such as levels of exercise and eating habits—may affect the amount of time required to pass a drug test.” Water-soluble material, like the traces of cannabis, is held in the fat cells. So those with higher levels of fat content store cannabinoids [more] readily than leaner folks, Rosado says.

Still, if your friend hasn't toked up at all in a month, he’ll probably pass a urinalysis test. While conducting research to assist drug courts and parole offices in 2005, Paul L. Cary, director of the Toxicology and Drug Monitoring Laboratory at the University of Missouri, found that cannabis detection after 30 days since last use happens, but it's rare. Frequency of use is also a factor. Cary found that most occasional cannabis consumers, or first-time users, retain detectable traces for only three to four days. Chronic users who have been smoking a few times a week have to refrain from their vape pens or glass pipes for 21 days, on average, to reach a point of pass-ability.


A 1999 study from researchers at Harvard University and McLean Hospital attempted to see how long cannabis traces remained in Willie Nelson-level king stoners, people who said they had smoked marijuana 5,000 times or more throughout their life. In what must have been a herculean show of restraint, 17 of these subjects agreed to abstain for 28 days. Five reached non-detectable levels in the first week. Four more produced clean pee by week two. Another two passed drug tests after the third week. Six peed detectable cannabinoids in week four. The study shows that people in the same usage category process their cannabis traces at different rates. But even serious potheads are usually clean after a month off the grass.

Is it legal for my employer to drug test me?

It's worth noting that this whole practice of peeing in a jar to maintain employment is a highly questionable leftover from the 1980s war on drugs, and hasn’t shown many definitive benefits to anyone but professional piss collectors at urinalysis labs.

In 1986, President Ronald Reagan signed an executive order requiring federal employees and some contractors to be tested. Many businesses followed suit: Testing as a precondition to employment became common across industries and those who operated other potentially hazardous equipment were tested continually and randomly. Drug testing peaked in 1996, when 81 percent of employers tested, according to a report from the American Management Association. That number diminished every year through 2004, the last year the AMA surveyed businesses, when it stood at 62 percent.


There is scant evidence that making employees or potential employees scared to smoke a joint on the weekend leads to a safer or more productive workplace. In 2007, the Substance Abuse and Mental Health Services Administration, a division of the National Institutes of Health, tackled the problem and concluded: “Workplace drug testing was implemented as an effort to deter substance abuse and its effects on productivity, health and safety in the nation’s workforce. To date, there is limited evidence about the effectiveness of this deterrent effect.”

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The practice is now complicated by the growing acceptance and legalization of marijuana (Quest Diagnostics, the Coca-Cola of pee analysis, reported slight increases in positive tests in the mid-2010s) and increasing usages of test-triggering medications. For some Rust Belt industries, drug testing policies have turned hiring into a major pain in the ass.

The Substance Abuse and Mental Health Services Administration report did find, unsurprisingly, that recreational users were less likely to apply at companies that tested—blocking those companies from a talent pool of the ten percent or so of the US population that uses cannabis regularly.

What happens if I fail my employer's drug test?

If your friend smoked in the last three or four days or had been on a binge in the last two weeks, it will probably show up in a urinalysis test. Even if it’s been a while since he last blazed, there are extreme cases where cannabinoids linger in the body for more weeks than an Italian’s government-mandated vacation time—as long as 77 days. Then he’ll have to face whatever penalties his employer imposes.

Sometimes, those penalties aren’t so bad. In fact, an employer’s reaction to a positive test is usually regulated by state laws and protections and those who would fire someone for failing a drug test are in a more perilous legal arena than those who just wouldn’t hire someone for their cloudy piss.

Some states, like Minnesota and Vermont, forbid an employer to fire someone for the first failed drug test if they agree to complete a rehabilitation program. There are, at some companies, penalties and precautions short of termination. One 2007 study found that two-thirds of companies that implemented drug testing also had some sort of employee assistance program for addiction, so your friend might just get volleyed to that—or taken off forklift duty for a while.

The bottom line

Employer drug tests are some retrograde bullshit. But unless you’ve toked up in the last week or you’ve been on a binge in the last three, you could (probably) pass the test and be back to stocking claw hammers and helping customers find the perfect power washer in no time. There’s no definitive way to tell, of course, but if you haven’t smoked at all in a month, odds are you’re probably good. If you fail, consult your state laws and company policy. It might not lead to a pink slip, but merely the ridiculous experience of going to rehab for pot to save your job.

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