How Long Does THC Stay In Your Urine?

At the dawn of the Reagan-era War on Drugs, California-based diagnostics company Syva Co. gave workplace testing a powerful weapon: a low-cost urine test capable of detecting THC metabolites.

Before 1980, only blood tests and expensive urine tests could detect marijuana in a user’s system. Syva’s innovation made widespread drug screening possible at a more affordable price, and it also extended the detection window by a considerable length of time. It did so by focusing on 9-carboxy-THC, which is the main metabolite of cannabis’s primary intoxicating ingredient (tetrahydrocannabinol, or THC) that is excreted in urine. Since these metabolites stay in the body for much longer than THC itself, the new test was more adept at catching cannabis users after a prolonged period of time.

The new test soon became the standard for workplace drug tests. As they became more widely deployed, people learned the specifics of how long THC stays in your urine — and the many factors that go into a positive result.

How Long Can THC Be Detected in Urine?

Many cannabis users have asked this question, and the answer is neither short nor simple. According to a National Drug Court Institute fact sheet on urine testing, “The duration of the urinary cannabinoid detection window is not settled science. The number of days, following the cessation of marijuana smoking, necessary for cannabinoids to become non-detectable using traditional drug testing methods is the subject of debate among forensic toxicologists and a matter of on-going scientific research.” In other words, it depends — on a lot of things.

Frequency of cannabis use is perhaps the most obvious factor, but since the test looks for the presence of THC’s metabolic products, the metabolism that creates these byproducts is also important. THC accumulates in body fat, which means detection windows can reach beyond 30 days for some chronic users, while other chronic users are negative within 24 hours. Hydration can help accelerate this process, as researchers estimate that 15 to 20 percent of THC in a person’s body ends up eliminated via urine.

The amount of THC in cannabis figures in, as well — a smoker of high-THC strains will test positive for a longer period of time than they would if they stuck to low-THC strains. It gets even more complex: edible cannabis products may stay in a user’s system slightly longer than smoked marijuana, and users with more body fat will retain more THC than slimmer users, although the amount of time users are positive is not related to their body mass index.

But what matters most? For all users, frequency of use is the biggest determiner. The level of metabolites in the urine of occasional users will drop below the detection threshold in as little as 2-3 days, while some studies have registered positive tests in chronic users as late as 90 days after the last consumption of THC, a window similar to hair tests. A 30-day period of abstinence is an appropriate window for most regular cannabis users.

For those who wonder if casual exposure to secondhand cannabis smoke could make them test positive, the answer is much easier: no.

What Exactly Does a THC Urine Test Look For?

In the United States, the most common cut-off for a positive urine test is 50 nanograms of THC metabolite per milliliter (ng/mL) of urine. A more sensitive cut-off is sometimes set at 20 ng/mL.

To discourage potential tampering with the sample, several other benchmarks are also evaluated by chemical tests. These include creatinine levels and specific gravity; pH and oxidizing reagents may also be evaluated.

Urine testing is done through an immunoassay-based test which employs a competitive binding mechanism. Immunoassays are quick and accurate tests used to signal the presence of a certain substance through its reaction with an antibody.

As a result, passing a THC urine test requires much more than having an acceptably low amount of THC in the sample, a fact that is often ignored by the makers of “quick cleanses” and other products marketed to those desperate to pass an upcoming test.

As Dr. Marilyn Huestis, a world-renowned expert on human drug testing and former Chief of Chemistry and Drug Metabolism at the National Institute of Drug Abuse’s Intramural Research Program, told cannabisMD in a phone interview, “Many products that are sold to beat the drug test are [diuretics]. Other products put something into the urine that changes the pH drastically or oxidizes materials, but boy are you in trouble if they find out that you’ve adulterated your test. There are tests to look for oxidants and things like that. And if they determine that, it is as bad as a positive test.”

Are There Any Tricks for Passing a THC Urine Test?

Urine tests, all agree, have their limits. As Huestis told cannabisMD, “The big issue is that they’re easy to adulterate.”

Just how easy remains a matter for debate. There are numerous proprietary methods for passing urine tests, with spotty clinical records to back up their efficacy. Despite the uncertainty, adulterants ranging from papaya enzyme to zinc sulfate are often found in so-called detox drinks.

Barry Cooper, a former drug enforcement agent who now works in “freedom activism” through his website NeverGetBusted.com, told cannabisMD, “Urine tests are easy to beat. There are two products that guarantee you pass your urine test — synthetic urine and detox drinks.

“Synthetic urine is the best but can only be used for employment, not probation. Probationers watch the pee go in the cup whereas employers don’t. If the tester is going to watch you pee, you can detoxify your system by purchasing a quality detox drink. These drinks work 100 percent if you follow the instructions exactly.”

Such claims would likely be greeted with skepticism from most testing officials, but there’s reason to believe that urine tests may be more fallible than one might expect. According to testimony presented before Congress by the U.S. Department of Health and Human Services, drinking water is one of the most effective ways of passing a urine test. And in 2005, Quest Diagnostics — one of the largest drug testing companies in the world — sent their Director of Science and Technology to testify before Congress in favor of criminalizing the production and sale of products aimed at influencing drug test results, so there does seem to be concern from the highest testing authorities that adulterants could successfully skew the results of a urine test for THC.

But overall, Huestis says the test tends to be effective. “We have tons of research to back it up, and we know what we’re doing when we do urine testing. It’s been around a long time.”