Drug tests can detect marijuana in your urine, blood, hair, and saliva.
Drug testing is a common practice in the United States. Current and future employers will often ask employees to undergo a drug test.
Drug tests for marijuana usually measure levels of THC or its metabolite, THC-COOH. Depending on the testing method, traces of marijuana can be detected for days, weeks, or even months after last use.
Urine testing is the most common way of screening for marijuana use. Other drug testing methods include blood tests, saliva tests, and hair follicle tests.
Let’s take a look at each of these drug testing methods, the detection period for marijuana, and the best ways to clear marijuana out of your system.
Drug Testing 101
What is a drug test and what does it check for?
A drug test for marijuana is the analysis of a biological sample to determine how much of the drug is in your system.
Testing for marijuana checks for levels of the active ingredient THC, or more commonly for its metabolite THC-COOH.
Marijuana contains hundreds of chemicals, but THC is the chemical or psychoactive component that affects mood, perception and behavior. THC-COOH is produced when the liver breaks down THC.
THC-COOH is the primary metabolite screened for in workplace drug testing.
What are the reasons for drug testing?
There are a number of reasons why drug testing for marijuana may be done. These include:
- Screening prior to employment
- Testing for those in security or military positions
- Safety precaution for those operating heavy machinery or vehicles
- Testing as a deterrent to prevent drug use in schools, companies and government departments
- Routine testing as part of a drug program
In the workplace, companies can conduct drug testing when an employee is:
- Believed to have been impaired at work
- Involved in an accident
- Returning to work after a substance abuse treatment program
Length of THC Detection
If you’ve used marijuana recently, you might be wondering — how long will I test positive for?
Unfortunately, there is no straightforward answer. The amount of time that THC stays in the body varies from person to person.
Tolerance is a big factor in drug test results, but so is a person’s history of marijuana use and the type of marijuana that was ingested. Other factors include fitness level, metabolism rate (energy you expend), gender, ethnicity, and diet.
There are also hundreds of different strains, all with different potencies and levels of THC. As a result, the detection period of marijuana can vary dramatically.
THC is fat soluble, which means it embeds itself into the body’s fat tissue. Those with higher body fat may store THC and its metabolites more readily compared to a person who is slim.
In fact, the slowest THC elimination is seen in fat tissue where it can be present days, weeks or months later, depending on the amount of marijuana used.
When it comes to testing positive for marijuana, the timeframes of detection can be very different for an occasional user compared to a frequent user.
Frequent marijuana users tend to retain THC metabolites in their fat tissues for much longer than occasional users.
THC-COOH has an elimination half-life (time it takes to exit the body) of about 4 days on average.
In a study of 52 volunteers, the average time it took to clear THC from the system was 4.9 days. In some volunteers, it took up to 18 days to eliminate THC-COOH from their urine.
In another study, infrequent users had positive urine samples for 48 to 72 hours after THC exposure. Heavy users, on the other hand, tested positive for 9 to 12 days on average.
Detection Window and Cutoffs
The detection window is the number of days that a person will test positive after last using marijuana.
Drug tests use a cutoff level to determine if a person is positive or negative for marijuana. Most urine tests use 50 ng/mL as a cutoff, meaning samples that test below the limit will be negative.
From a drug testing perspective, it’s not necessarily about the time that the active ingredient stays in the system, but more about the number of days until the last positive test.
In other words, you can still have traces of marijuana in your system and test negative as long as you are below the cutoff.
Types of Drug Testing
Marijuana Urine Tests
Urine testing is the most common way of screening for marijuana use. Urine samples are usually collected on-site and then sent to a laboratory to be tested.
Urine tests detect THC-COOH, which is a metabolite of THC. It is produced when the liver breaks down THC and stays in the body much longer.
The most common cutoff for urine tests is 50 ng/mL, while 20 ng/mL and 100 ng/mL are less common.
No one can really say how long you will test positive for marijuana, since the rate of THC metabolism varies from individual to individual. However, studies provide some insight on the number of days it might take to pass a urine test.
Occasional or first time users who smoke marijuana will most likely test positive for 1 to 3 days, according to the National Drug Court Institute (NDCI). But infrequent users should test below the 50 ng/mL limit after 4 days.
Frequent marijuana users can expect to test positive for 7 to 10 days following their last use. Most frequent users should pass a urine test at the 50 ng/mL limit after 10 days.
But there is no guarantee on the detection window of marijuana, particularly for a heavy or chronic user.
Some users may test positive on a urine test for more than a month after last use. In one extreme case, an individual with a ten-year history of cannabis use tested positive (above 20 ng/mL) for 67 days after quitting.
Marijuana Blood Tests
Unlike urine tests, blood tests measure active THC and metabolite levels in the bloodstream to determine if an individual has recently used marijuana.
Blood tests are generally done after a traffic accident, an autopsy when someone has died, or to check for intoxication.
Levels of THC in the blood peak rapidly after smoking marijuana and can reach 100 ng/mL or more within minutes. However, 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.
However, taking blood is invasive, meaning that a needle has to be used to draw blood, which is why this type of test is used less frequently than others.
Blood sample studies have shown a connection between high THC levels and driving impairment. In Colorado, drivers cannot have more than 5ng/mL of THC in their blood.
Marijuana Hair Tests
Hair tests have proven to be more accurate than other drug tests. Hair testing also provides the longest window of detection compared to other screening methods, covering a span of approximately 3 months.
THC reaches the hair follicles through the blood vessels in the scalp and is deposited in the hair shafts. Once there, THC will remain on the hair as it grows.
Just a small sample of hair is necessary for testing. A hair strand of about 1.5 inches or 3.9cm covers a time span of 90 days, which can show a pattern of single or repeated marijuana use.
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. Studies show that THC can also be incorporated into the hair through secondhand smoke.
Hair testing can be a reliable method but it is more expensive than other tests. The typical cutoff for hair follicle tests is 1 pg/mL.
Marijuana Saliva Tests
Saliva testing is one of the newest methods of testing for marijuana. It is less expensive and more convenient than other tests that detect recent use.
Saliva samples can produce positive results within the first 24 hours of marijuana use. In one study, the detection period was found to be 12 hours on average.
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 can detect THC 24 hours after marijuana intake, and THC-COOH for a few days longer. The typical cutoff level for saliva swab testing is 2 ng/mL.
Marijuana Sweat Tests
Sweat testing is a relatively non-invasive way to monitor drug exposure using a patch that is applied to the skin for 10 to 14 days. It is often used in drug treatment, criminal justice and employment programs.
This type of testing has certain limitations since the amount of perspiration can vary between individuals. THC levels in sweat also depend on the environment, temperature and level of physical activity.
Sweat patches can detect marijuana use just a few hours before its removal. Results of one study showed that daily marijuana users will excrete THC into sweat above the cutoff of 1 ng/patch for weeks after stopping use.
There are limitations however, as the sensitivity of the patch to detect drug use is dependent on the amount of THC consumed.
How To Get THC Out of Your System
So now that you know the basics about marijuana and drug testing, the next question you might ask is how do you eliminate THC from your system?
There are several methods that people often try, but few have been proven to work. Overall, the only truly effective method is abstaining from marijuana prior to a drug test.
Drinking extra water may help to clear the excess THC metabolites from your system, but urine that is too diluted may be rejected. Finally, exercise can help eliminate THC that is stored in your body’s fat tissues.
Abstinence (Best method)
Of course, the easiest way to avoid testing positive is to not use marijuana, or at least abstain from it prior to a drug test.
The half-life of THC metabolites is about 3-4 days for the average person or 7-10 days for a regular user. For a heavy user, it could take at least 10 days or up to 60 days for previous THC levels to clear. So, know your limits and adjust accordingly.
Urine Dilution (Might work)
One of the most common ways of flushing THC out of your system is to drink excessive amounts of water. This is also one of the few methods scientifically-proven to work.
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 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.
Drinking a lot of water naturally dilutes anything found in the urine, but you shouldn’t drink more than 2 liters a day. So, it’s important to hydrate carefully.
Drinking too much water can be dangerous to your health and even cause death. Also, urine samples that appear too diluted may be identified and rejected by testing labs.
Exercise (Might work)
Exercising may help speed up detoxification, but efforts to sweat out THC could actually result in a spike in THC and metabolite levels as they exit the body.
Exercise helps burn body fat and since THC is stored in fat cells, it may help eliminate some THC from your system.
However, exercise should be stopped at least 24 hours to a few days before a drug test to reduce the amount of THC being released into the bloodstream. THC that is stored in fat cells cannot generally be detected.
Other Possible Methods
- Fasting is another way of burning body fat that might help when it comes to passing a drug test.
- Taking Vitamin B may also work along with drinking extra water. As an excess of water in the system can make urine clearer, taking Vitamin B can add to creatinine levels and the color of the urine.
- Drinking a diuretic like cranberry juice or coffee might also help to encourage urination, but there is little evidence that it helps with passing a drug test.
- Using an over-the-counter diuretic may help but can be detected.
- Excuses don’t cut it. It is difficult to challenge a positive test outcome no matter the reason.
- Trying to spike or spoil a urine sample with an adulterant like eye drops, detergent, nitrites, glutaraldehyde, oxidizing agents such as bleach and hydrogen peroxide, vinegar, lemon juice or other commercially sold products can easily be detected by testing labs.
- There is no evidence that herbal teas, urine cleansers/detoxes, goldenseal, niacin, lecithin, activated charcoal or vitamin C will help with passing a drug test.
- Trying to substitute a urine sample is deception. Testing labs will usually measure various parameters (such as pH levels and temperature) to ensure that a urine sample is normal.
- Using pain relievers like ibuprofen will not interfere with a drug test.
Warning: Passing or cheating on a drug test is extremely difficult and could have legal repercussions. You should always be aware of your company or potential employer’s policies regarding drug testing. None of these suggested methods are guaranteed to work.
Commonly Asked Questions
What is a false positive result?
Results can be ‘false positive’, meaning that the drug test reads positive even though there are no traces of marijuana in your system.
A false positive can happen (no drug test can be 100% accurate), but rarely does. Current laboratory techniques tend to be reliable in showing conclusive or positive results when it comes to the presence of THC.
Drug testing usually involves a two-step process: initial and confirmatory testing. The initial test is called an immunoassay and is often used as a screening method.
If the immunoassay is negative, then the sample is reported as negative and no further action is required. If the immunoassay is positive, the sample is tested again using a more sensitive test called gas chromatography-mass spectrometry (GC-MS) to confirm the results.
This second round of testing greatly reduces the chances of a false positive.
Can secondhand smoke lead to a positive test?
Yes, studies show that it is indeed possible to test positive for THC following secondhand exposure to marijuana 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 50ng/mL).
Traces of marijuana have also been found in the hair, oral fluid, and blood of people who have been exposed to secondhand smoke.
However, there is very little THC exhaled back into the air from someone smoking marijuana. So, it would take a lot of secondhand exposure to test positive on a drug test, and the chances of it happening are slim.
Does CBD show up on a drug test?
No. Cannabidiol (CBD) is a non-psychoactive component of marijuana. Drug tests are designed to detect THC or THC-COOH and not CBD.