How Long Does THC Stay in Your System?

A COMMON QUESTION for cannabis consumers, especially those who are concerned about workplace drug testing, is how long THC lingers in the body. Before we dive into a suitable answer, it’s important to keep in mind two key caveats:

1. There are many different kinds of drug tests available, which have varying levels of sensitivity and time periods to detect cannabis in your system.

2. Wide-ranging patterns of usage as well as a unique biology for each individual make the calculation of a concrete detection window (the number of days after ceasing usage that a drug test will continue to be positive) even more complex.

How Do Drug Tests Work?

About forty to fifty million drug tests are conducted by employers each year, which analyze biological material including urine, hair, blood, saliva, breath, sweat, and even fingernails. When cannabis is consumed, THC levels temporarily rise in the body, which are detectable by blood tests from several hours up to a day after a single usage. Although these levels drop significantly after a few days, there are still other means of determining recent usage.

THC, CBD, and their metabolic by-products (called metabolites) are lipid-soluble and accumulate in fat reserves throughout the body. These molecules are then slowly released over time, resulting in a considerably longer time period for the body to purge itself of marijuana traces compared to other recreational drugs, especially for chronic users.

While each drug test has its advantages, urine tests tend to be the test of choice for most private employers and are the sole test recommended by the Substance Abuse and Mental Health Services Administration (SAMHSA), a branch of the U.S. Department of Health and Human Services that sets standards for drug testing of government employees. Urine screens do not directly measure the amount of THC present, but rather the levels of the metabolite THC-COOH.

Once a specific test is selected, the experimenter must then choose its sensitivity, or the cutoff concentration of THC-COOH above which a test is considered positive. The most common cutoff for most urine tests is 50 nanograms per milliliter (ng/ml), but cutoffs can be as low as 15 ng/ml and as high as 100 ng/ml, each of which result in widely different detection windows.

Despite the fact that SAMHSA sets standards that regulate these urine tests, the vast variability in cannabis use as well as individual differences in biology and genetics make it difficult to develop specific time windows for detection.

How Long Does Cannabis Stay in Your System?

Each of us has a unique metabolism that processes cannabis at a different rate, further complicating the picture. Even among people of the same gender and age, individual lifestyle choices such as levels of exercise and eating habits may also affect the amount of time required to pass a drug test (those with higher levels of fat content store cannabinoids more readily than leaner folks).

While detection times in excess of thirty days do occur for some, they are largely an exception. For example, a 1989 study of chronic users showed a maximum detection window of twenty-five days at a sensitivity of 20 ng/ml. Yet only one subject tested positive after fourteen days, and it took an average of just 9.8 days before cannabinoid levels were no longer detectible. And while a 1984 study testing chronic users at a cutoff of 50 ng/ ml showed a maximum of forty days to get clean, eight out of the ten subjects needed only thirteen days to show their first negative.

These findings are general recommendations, not hard facts; actual detection windows will vary based on a number of factors outlined in this chapter.

Chronic^* users at the standard 50 ng/ml cutoff: unlikely detection for longer than 10 days after last smoking session

Chronic users at 20 ng/ml: unlikely detection for longer than 21 days after last smoking session

First-time/occasional^* users at the standard 50 ng/ml cutoff: unlikely detection for longer than 3 to 4 days after last smoking session

First time/occasional users at 20 ng/ml: unlikely detection for longer than 7 days after last smoking session

Factors That May Impact Drug Test Results

There are instances where individuals fluctuate between positive and negative tests over a period of time. A couple of factors may contribute to a range of variability in positive THC tests:

Dehydration—if a person becomes dehydrated, it concentrates the urine, which can increase the chance of a positive test

Exercise—working out breaks down fat cells and releases THC, which can spike levels detected in a drug test

Because standard urine testing only analyzes metabolites of THC, those who consume CBD or CBD hemp oil have very little risk of testing positive. Hemp oils contain very small amounts of THC. If you use an extraordinarily large amount of cannabinoid-rich oil products (greater than 1,000 to 2,000 milligrams each day), you might show a positive test on the initial urine screen, which is susceptible to cross-contamination from other cannabinoids. However, this initial “false positive” would not hold up to the more rigorous second round of confirmatory testing, which specifically measures THC-COOH.

Can You “Cheat” a Cannabis Drug Test?

Is there anything you can do to prevent a positive test or speed up the detoxification process?

Although abstinence is an obvious initial answer, it may even be dangerous to hang out with friends who are smoking. In a 2015 study, a small group of participants were exposed to secondhand smoke in both ventilated and unventilated rooms. Some participants who sat in the unventilated room tested positive for THC-COOH, with concentrations in urine exceeding 57 ng/ml. While it’s not a given that being exposed to secondhand cannabis smoke will result in a positive drug test, it is possible, so if you’re subject to drug testing and are surrounded by a group of people smoking cannabis in a confined space, you should leave.

Regular consumption or use of commercially made hemp foods (such as seeds, cooking oil, cereals, milk, granola) or hemp products (lotions, shampoos, lip balms, et cetera) will not show a positive result for THC on a drug test. Hemp-based foods and hemp body products commercially produced and sold in the United States are not legally allowed to contain THC. If a laboratory-tested hemp product did happen to contain trace amounts of this compound, it would be in such small quantities that it would likely require exorbitant amounts of ingestion or use for it to even remotely begin to show up in the smallest amount on a drug test. With that said, consuming noncommercially produced hemp foods, hemp-based oils, or using homemade hemp-based products may risk a positive test result. Nonfederally regulated foods and products, like those purchased from a dispensary, farmer’s market, or even products bought online, do not necessarily follow any sort of federal food safety guidelines or Food and Drug Administration regulations. When purchasing these types of hemp products, make sure you use caution and ask questions about how they were made and whether they were tested before being packaged.

How to Get Rid of THC in Your System

For those who are able to quit, one common technique is to flush out your system by drinking a lot of water. This can be a good approach, as dehydration will increase the concentration of your urine and could increase your chances for a positive result. If your urine is diluted too much, however, it will automatically invalidate the results and you will have to repeat the test, so hydrate carefully.

A potentially more effective tactic for speeding up the detoxification process might be cutting back on the burgers and hitting the gym. People with more fat will have more tissue for cannabinoid storage, so they might experience a slightly longer window of detection. Fasting will burn fat, which will in turn release more cannabinoids.

Make sure to give your body enough time to clear out these stored cannabinoids, as exercise or fasting will likely result in a transient spike in measurable THC metabolites as they exit the body.

If you know you have an upcoming drug test, not all hope is lost. Given the current detection windows for standard cannabis tests, it’s likely you will be able to pass a urine test as long as you are not an extremely heavy user and are given sufficient advance notice.

Many who are facing a drug test but are unwilling to fully give up cannabis turn to synthetic cannabinoids in the hopes of cheating traditional tests. These alternatives, commonly referred to as “K2” or “spice,” are unpredictable, showing side effects ranging from nausea to seizures that have caused a spike in overdoses and even deaths. And many private companies now include tests for synthetic cannabinoids in their repertoire, making this approach both dangerous and futile. Bottom line: Stay far, far away from synthetic cannabis. It’s dangerous.

Others who continue to smoke may attempt to tamper with their urine, adding chemicals such as pyridinium chlorochromate or peroxidase that eliminate THC-COOH in the sample. Most testing agencies, however, will screen for these compounds, and being caught is often just as bad, if not worse, than a positive test.