The amount of time that marijuana stays in your body depends on many factors, such as how often you smoke and your metabolism rate.
Drug testing is often used in the workplace to screen potential hires and current employees for illegal substance use.
You might also be asked to undergo a drug test if you are suspected of impaired driving, under probation or as part of a drug rehab program.
The problem for marijuana users is that compared to other recreational drugs, marijuana stays in the body for much longer.
THC, the active ingredient in marijuana, is fat-soluble and remains in the body’s fat cells. As a result, it can take a long time for THC to be eliminated by the body, especially if you use marijuana regularly.
How Do Marijuana Drug Tests Work?
Drug tests look for signs of marijuana use by measuring levels of THC or THC metabolites in your system.
There are a number of ways to test if THC is present in a person’s system. Urine testing is by far the most common method of drug testing today. Urine samples are usually collected on-site and then sent to a laboratory to be tested.
THC can also be detected in hair, blood and saliva samples. Hair testing provides a longer window of detection than urine and can detect drugs taken within the past 90 days.
On the other hand, blood and saliva tests can only show if marijuana was used in the past few hours. Drivers may be asked to undergo a blood or saliva test if they are suspected of driving while impaired.
How Long Does THC Stay in Your Urine?
Urine testing (also known as urinalysis) is the most common method of screening for marijuana use. In the United States, current and future employers will often ask you to undergo a urine test.
But how long will marijuana show up in your urine after you stop smoking? Unfortunately, the only accurate answer is: it depends.
THC vs. THC-COOH
THC is the active ingredient in marijuana and the chemical responsible for the high. However, urine tests detect a different chemical called THC-COOH.
THC-COOH is a metabolite of THC. It is produced when the liver breaks down THC and stays in the body for much longer.
The most common cutoff level for THC-COOH used by drug screening companies is 50 ng/mL. Less common cutoff levels are 20 ng/mL and 100 ng/mL.
Length of Detection Period
No one can really say how long you will test positive for marijuana, since the rate of THC metabolism varies per individual.
Factors that affect how quickly THC is metabolized include exercise, eating habits and your body fat percentage. Frequency of use and the amount of marijuana consumed can also alter the length of time that your body retains traces of THC.
Nevertheless, studies provide some insight into how long the average individual will test positive for marijuana in their urine (see below).
Someone who smokes occasionally or for the first time will likely test positive for 1-3 days afterward, according to a review by the National Drug Court Institute (NDCI).
But by the end of 4 days, infrequent cannabis users should be safely below the 50 ng/mL threshold.
“For occasional marijuana use (or single event usage), at the 50 ng/mL cutoff level, it would be unusual for the detection of cannabinoids in urine to extend beyond 3-4 days following the smoking episode.”
Studies suggest someone who smokes marijuana often can expect to test positive for 7-10 days following last use. According to the NDCI, after 10 days, most frequent users should pass a urine test at the 50 ng/mL threshold.
“Based upon recent scientific evidence, at the 50 ng/mL cutoff concentration for the detection of cannabinoids in urine, it would be unlikely for a chronic user to produce a positive urine drug test result for longer than 10 days after the last smoking episode.”
However, there’s no guarantee that a heavy cannabis smoker will be free of THC metabolites after 10 days. Studies show it’s possible for some users to test positive for up to a month after last use.
In one extreme case, a person who reported using cannabis heavily for over 10 years managed to test positive (>20 ng/mL) for up to 67 days after last use.
How To Pass A Urine Test
There are many products that claim to help with passing a drug test by flushing out any traces of marijuana from your system.
Often sold as urine cleansers and detoxifiers, these products may contain various herbal ingredients or non-toxic chemicals, such as activated charcoal and lecithin. Unfortunately, while many have attempted to use these products, none have been proven to work consistently.
Other strategies for passing a urine test include tampering with the urine sample by adding adulterants or substituting the sample with clean urine.
Common adulterants that may be added to urine samples include nitrites, glutaraldehyde, oxidizing agents (such as bleach and hydrogen peroxide), vinegar and lemon juice.
Once again, these attempts to fool a drug test are highly risky and often fail to achieve the desired effect. Most drug testing companies take precautionary measures to identify samples that have been tampered with. For example, labs will often test for traces of adulterants and measure various parameters (such as pH levels) to ensure that the urine sample is normal.
Diluting Your Urine
Diluting your urine by drinking an excessive amount of liquid is one strategy that might actually help with passing a drug test.
In fact, some studies have found that drinking large amounts of water prior to a urine test can lower the THC-COOH levels in your urine sample and lead to a negative test result.
To employ this strategy, it is recommended that you drink as much water as possible an hour or two before taking a drug test. Diuretics such as coffee and cranberry juice may also be taken to help stimulate urine production.
However, this method is not foolproof, since drug testing companies will often screen urine samples for signs of dilution.
Urine that is too diluted may be identified and rejected by the testing lab as possibly being tampered with. Still, this could buy some time for a retest, depending on the circumstances.
How Long Does THC Stay in Your Blood?
Unlike urine tests, blood tests are used to measure the amount of active THC in your body. After smoking, THC enters the bloodstream immediately and reaches peak levels of over 100ng/mL within the first few minutes. But THC levels quickly drop to single digits after the first hour.
Because of this rapid decline, THC blood levels are a good way of measuring intoxication and driving impairment. In Colorado, drivers cannot have more than 5ng/mL of THC in their blood.
Studies show that following a single session of marijuana use, THC levels drop below 1ng/mL within 3-12 hours.
Heavy users seem to retain THC in their blood for longer, possibly due to slower absorption of the compound into other parts of the body. Studies show that heavy marijuana users may test positive (>1ng/mL) for THC in their blood up to 7 days after last use.
How Long Does THC Stay in Your Saliva?
Saliva tests measure THC levels in your oral fluid. Like blood tests, saliva tests are used to establish if marijuana was used within the past few hours. Saliva tests are most commonly used as a roadside test for driving impairment.
The linings of the mouth absorb THC when you smoke and are the source of THC that remains in your saliva.
Saliva tests are much less invasive and easier to administer than blood tests. However, they are relatively new and less common than blood tests.
Studies show THC can be detected in saliva for up to 24-34 hours after marijuana use. In one study, the detection period was found to be 12 hours on average. The typical cutoff for saliva tests is 1-2ng/mL of THC.
How Long Does THC Stay in Your Hair?
Hair drug tests can detect THC and THC metabolites in a person’s hair. Hair tests provide the longest window of detection compared to other drug tests, covering a span of approximately 90 days.
THC and THC metabolites can travel from the bloodstream and bind to the bulb or shaft of your hair and remain on the hair as it grows. Studies show that THC can also be incorporated into the hair through secondhand smoke.
Hair tests usually measure levels of THC-COOH instead of THC since THC-COOH is not present in marijuana smoke. Hair tests typically look for THC-COOH using a cutoff of 1 pg/mL.
Regular marijuana users are more likely to test positive on a hair test due to the build up of THC-COOH in their hair over time.
Can Secondhand Smoke Cause a Positive Test?
Studies show that it is indeed possible to test positive for THC following secondhand exposure to marijuana smoke.
Traces of marijuana have been found in the hair, oral fluid, blood and urine of people who have been exposed to secondhand smoke. One study found that individuals who sat in a small, non-ventilated room with someone who was smoking marijuana could test positive on a urine test above the 50ng/mL limit.
However, the general consensus is that only in extreme cases will secondhand smoke result in enough contamination for a person to test positive on a drug test.
Still, the safest bet is to avoid secondhand exposure to marijuana altogether if you plan on taking a drug test in the near future.