As medical marijuana has become legal in many states, and recreational cannabis has been approved in four states and Washington, D.C., employers have started to consider new testing efforts to ensure their employees are showing up sober. The problem is that even if someone isn’t high, remnants of marijuana can still show up for a significant time period after smoking their last joint. While other drugs like alcohol, cocaine, and heroin disappear in your body’s system after a day or so, marijuana can linger for much longer. How long, exactly? Unfortunately, it depends on numerous personal factors.
Unfortunately, urinalysis — the most common form of drug testing in most workplaces — does not detect THC, the psychoactive component in marijuana that actually creates the “high.” Instead, it detects nonactive metabolites from the drug, which tend to stay in the body for much longer. Those metabolites are filtered out by your body but are fat-soluble, which take longer to process than water-soluble components. That also means that factors like your weight, diet, and exercise habits can impact how long the remnants of the drug stay in your body, long after the high is gone. Like most drugs, how often you use cannabis products is also a variable.
Occasional users (Once per week or less): Stays in system for 1-5 days after the last use
Regular users (More than once per week): Stays in system for 1-3 weeks after last use
Heavy users (Multiple times per day, or regular use for a prolonged period of time): Can stay in system up to 4-6 weeks after last use
If you’re taking a urine test, the lab technician is looking for a certain concentration of those metabolites. Typically, the threshold for a positive test — and likely a rough conversation with your boss — is 50 nanograms per milliliter (ng/ml) or more.
A few things to note: At that level, using the excuse of passive smoking (e.g. “My roommate smoked last night, but I didn’t,”) won’t cut it. Only extreme circumstances — like getting locked in a closet with several heavy pot users for hours at a time — would potentially cause enough exposure to register a positive urine sample. NORML notes that passive smoking could cause positive readings at 25 ng/ml or lower, but it still might not be a valid cause.
Even if you legally smoke marijuana, you could still be fired for a positive test result — no matter which state you live in. With that in mind, it’s your best bet to turn in a clean sample, if you’re given advance notice. Most sites caution you to steer clear of self-advertised “cleansing” products, as most of them aren’t proven to be effective and can be harmful to your health. If you have a few weeks to get clean, the best option is to drink plenty of water, eat lean and healthy foods, and perhaps drink natural diuretics like cranberry juice or coffee.
NORML advises against using marijuana on the job, but if you need to take a test and used marijuana recently, the site recommends drinking as much water before the test as possible, to dilute the concentration of any marijuana-related metabolites. However, some lab techs will reject a sample if it’s too watery. Taking 50-100 milligrams of vitamin B-2 can help to color the sample so it doesn’t appear too diluted — though it’s not a foolproof solution.
Of course, the safest option is to abstain from marijuana use completely in the weeks leading up to a drug test, so you don’t need to have an uncomfortable conversation with your boss or potential HR manager. Even if you’re using marijuana within the confines of your state and local laws, a positive test result could spell trouble for your career.