- To screen for and/or confirm marijuana use
- As part of a panel of tests to help detect drug use, impairment, intoxication and/or overdose
- To monitor for drug abuse
- To monitor compliance with prescription drugs
Marijuana (THC) Testing
- During medical screening, such as upon admission to the emergency room or when pregnant or after giving birth
- When being treated for chronic pain or for cancer
- During random drug screening in the workplace or during the hiring process
- As part of a drug rehabilitation program or upon court order
- To test for impairment, such as during a traffic stop, or after an accident
- A random urine specimen is the most commonly tested sample for marijuana. Urine is collected in a clean, sterile container.
- Sometimes, saliva is collected in an absorbent pad or swab placed between the lower cheek and gums. This technique is increasingly used in workplace marijuana testing.
- Other types of samples that are used less frequently include blood and hair. For newborns, samples may include the umbilical cord or meconium, a newborn's first bowel movement. For more information on these, see Common Questions below.
Prior to testing, declare any prescriptions you are currently taking, including those for medical marijuana.
If saliva is to be collected for testing, you typically should not put anything in your mouth for the 10 minutes prior to the collection of the sample. Follow the directions provided with the sample container.
Cannabis, also referred to as marijuana, is a plant of the species Cannabis sativa that has psychoactive effects. Marijuana contains many chemical compounds that interact with the body, called cannabinoids. The main mind-altering cannabinoid in marijuana is THC (delta-9-tetrahydrocannabinol). The body breaks down THC into several inactive metabolites (e.g., THC-COOH, 11-nor-carboxy-delta-9-tetrahydrocannabinol). Since the metabolites of THC stay in the body for a longer period of time than THC does, most marijuana testing detects the presence of THC-COOH or other metabolites in urine. Some tests also detect the active compound, THC, for example when marijuana testing is done using blood or saliva.
Marijuana leaves can be smoked, prepared and eaten in food products, or ingested as a tincture. Smoking or ingesting marijuana causes a faster heartbeat and pulse rate, bloodshot eyes, and dry mouth and throat. It may cause short- and long-term effects, including impaired short-term memory, altered sense of time, decreased ability to concentrate, altered reaction time, decreased coordination, increased risk of psychosis, and cyclic episodes of nausea, stomach pain and vomiting. Marijuana use impairs driving ability, and accident risk greatly increases if the driver is also drinking alcohol. Marijuana today has higher THC concentrations than in the past, which can lead to greater levels of impairment.
Marijuana is the most commonly used illicit substance as defined by U.S. federal law. However, marijuana is used both recreationally and medicinally, and its use has been legalized in a number of states and Canada.
Marijuana as medicine
Some people use marijuana to treat a variety of conditions. Due to legal restrictions on marijuana, its therapeutic effects and safety have been difficult to research.
Natural cannabis may be obtained in some states with a medical marijuana card, an identification card issued by the state with a healthcare practitioner's recommendation. It allows a patient to obtain, possess, and/or grow marijuana for medicinal use. The process for obtaining these cards varies by state.
Synthetic forms or purified forms of THC and other cannabinoids are available as prescription medications that can be taken by mouth, inhaled, or sprayed under the tongue.
- Dronabinol and nabilone are two drugs approved by the U.S. Food and Drug Administration (FDA) that contain THC. They are sometimes prescribed to treat chemotherapy-associated nausea that does not respond to standard treatments.
- Cannabidiol (CBD) is a compound related to THC that is a product of the marijuana plant. It is available in liquid form (CBD oil) as an FDA-approved medication that may be used to treat pain and inflammation and some epileptic seizures. Some "herbal supplements" also contain CBD but are not regulated by the FDA. Unlike THC, CBD is not intoxicating—it does not make people "high." However, because CBD is derived from the marijuana plant, it may contain variable amounts of THC.
- Nabiximols is a marijuana-derived prescription drug that contains THC and CBD. It may be used to treat muscle control problems in people with multiple sclerosis (MS). Though this drug has not been approved by the FDA, it has been approved for use in Canada, the United Kingdom, and some European countries.
Anything that contains THC has the potential to be detected as THC or THC-COOH in a marijuana test. In medical cases, drug testing results are typically reported to the physicians who ordered the tests and they interpret the meaning of results in the context of the medical cases. To aid the interpretation of results, patients should notify their physicians of any over-the-counter or prescription medications (including marijuana) or supplements they are taking.
Marijuana laws and policies
Drug testing policy for THC can become confusing due to conflicting state and federal laws and policies. Marijuana is a Schedule 1 drug according to U.S. federal law. The government considers Schedule 1 drugs to have high potential for abuse, lack evidence of safety and effectiveness, with no currently accepted medical use in the U.S.
Since 1986, U.S. federal employees and employees in federally-regulated jobs that affect public safety like transportation and air traffic control have been prohibited from using illegal drugs. In U.S. federally regulated tests, no marijuana use is considered legitimate, except in the case of prescription synthetic THC, such as dronabinol. Private employers not under federal drug testing regulations are free to determine their own drug testing policies and may or may not test for marijuana use.
If someone is given a drug test for legal or employment purposes while taking a prescription form of THC, they should report their prescription to the physician who will review the test results (Medical Review Officer or MRO) and/or list it under 'prescriptions' in the appropriate space on the specimen collection form. Positive drug testing results that are due to prescription medications may be reported by the MRO as "negative."
To test for marijuana, healthcare practitioners may send urine samples to a laboratory for screening or they may perform a test in their office. Testing may be performed with point-of-care tests, which are typically small strips that are dipped into the urine and interpreted by the appearance or absence of a colored line on the strip.
Positive screening tests for marijuana are presumptive. This is because all drug screening tests have the potential for false-positive results. Therefore, screening tests that are positive are often confirmed with a second test, which is referred to as a confirmatory test. Confirmatory tests are usually more sensitive and specific than screening tests. Confirmatory testing is usually performed with an instrument called a mass spectrometer. Types of mass spectrometry tests used for confirmatory testing include gas chromatography/mass spectrometry (GC/MS) and liquid chromatography-tandem mass spectrometry (LC-MS/MS).
Additional testing may also be performed to identify whether any substance has been added to the urine sample, such as water, bleach, or other types of chemicals (adulterants) in an attempt to interfere with the test result. If adulteration is suspected, the test may be reported as invalid or adulterated.
Urine samples may also be identified as dilute. Dilute urine may be produced if an individual drinks large amounts of water or other liquids prior to testing. Dilute urine may also result from some medical conditions. If an individual adds liquid such as water to a urine sample, this may also cause dilute urine. It may not always be possible to determine how the urine was diluted. If the urine is so dilute that the results are not reliable, the test may be reported as invalid or adulterated.
How is the test used?
Marijuana testing is used to detect the presence of the plant’s active chemicals or their breakdown products (metabolites), most commonly in urine or saliva. Marijuana testing may be used to screen for and confirm the presence of THC or THC metabolites that indicate marijuana or prescription cannabinoid use. Most marijuana tests look for an inactive metabolite of THC (THC-COOH), which stays in the body longer than THC itself.
Marijuana testing may be used for:
Marijuana may be included in a panel of drug tests used for medical screening. This testing is used to determine what drugs or combination of drugs a person may have taken so that the person can receive proper medical treatment. With marijuana legalization in some areas, some clinics, emergency rooms and hospitals are no longer including marijuana testing in their drug testing panels.
A healthcare practitioner may order drug testing for medical reasons if an individual:
- Is being treated in an addiction recovery or chemical dependency program
- Is being treated for chronic pain, to ensure that the person is taking mediation as prescribed
- Experiences symptoms that may be drug-related or shows signs of intoxication, such as unconsciousness, nausea, delirium, panic, paranoia, increased temperature, chest pain, respiratory failure, seizures, and/or headaches
- Is involved in an accident that an emergency room physician suspects may be due to drug intoxication
- Is suspected of drug abuse or is known to use illegal drugs
- Is a candidate to receive an organ transplant
- Is being treated for cancer
- Is pregnant or has recently given birth, especially if she is thought to be at risk for drug abuse or has a newborn baby exhibiting certain characteristic behaviors
- Is an applicant for a life insurance policy, as part of an overall health evaluation
For a more in-depth discussion of medical drug screening, see the article Emergency and Overdose Drug Testing.
Legal, Forensic and Employment Testing
Drug testing for legal, forensic, or employment purposes differs from medical testing in sample collection procedures. Sample collection for forensic testing is strictly controlled, with the custody of a sample continuously documented to maintain a legal "chain-of-custody." After a sample is provided, it is closed and secured with a tamperproof seal. A custody and control form accompanies the sample throughout all handling, testing, and storage. This creates a continuous legally binding record for the sample. Test results are usually reviewed by a specially trained and licensed physician called a medical review officer prior to reporting.
Examples of this type of testing include:
- Court-mandated testing for someone who has been convicted of illegal drug use
- Testing or monitoring of a parent in a child custody case
- Forensic toxicology testing using a variety of body fluids and tissues that may be tested during a crime investigation; the goal may be to determine whether marijuana was a contributing factor to an accident or crime, such as DUI (driving under the influence).
- Some athletic programs may test for marijuana as part of a general toxicology screen to detect performance-enhancing drug abuse in athletes.
Marijuana testing may also be required by an employer. This is also referred to as "workplace drug testing," a specific type of forensic testing. It may be done prior to employment, on a random basis, following an accident, or if an employer has a reasonable suspicion that an employee is using illegal drugs.
Employment drug testing is common. It is required for employees of the U.S. Department of Transportation, military personnel, and other federal employees, and is an accepted practice in many other industries.
For additional information on this type of testing, see the article on The World of Forensic Laboratory Testing.
When is it ordered?
Marijuana testing may be ordered by a healthcare practitioner, usually as part of a drug testing panel, during a medical evaluation or addiction treatment when a person is known or suspected of substance abuse or when a person has signs and symptoms that suggest drug use, including confusion or otherwise abnormal or dangerous behavior. Testing may also be ordered as part of general health screenings prior to the start of some insurance policies.
Legal, Forensic or Employment Testing
Forensic THC testing is performed when an employer or legal entity needs to determine if a person may have used marijuana. It may be ordered randomly or routinely as part of employment screening, during the hiring process, or part of broader drug testing in legal or forensic scenarios, such as after an accident. Testing may be ordered at random to satisfy court-ordered monitoring or probation requirements.
What does the test result mean?
Just as for other types of lab tests, both screening and confirmatory tests are interpreted based on a defined cutoff level (e.g., 50 nanograms per milliliter (ng/mL) for urine samples). If a drug is not present, or if the drug is present at a concentration below the test cutoff, the test will be reported as "undetected," "absent" or "negative." If a drug is present at a concentration equal to or above the cutoff, the test will be reported as "detected," "present", "presumptive positive" or "positive."
A positive or detected initial THC screening result means that the person tested may have used marijuana. Since screening tests are not definitive, confirmatory testing is typically done to verify the results. A positive confirmatory test means the person had THC or THC-COOH in their body when the sample was collected, but it does not confirm when THC was used or ingested.
Testing urine for THC cannot be used to determine the source of THC or its metabolites, time of exposure, amount, or the person's level of impairment.
A negative result does not necessarily mean that the person did not use marijuana. The person's THC levels may be below an established cutoff or the THC may have been already metabolized and eliminated from the body.
Detection times for marijuana vary widely depending on an individual's metabolism, the dose, and frequency of use. Testing can indicate use anywhere from 3 days to more than 30 days prior to testing. Chronic, heavy users of marijuana may test positive for even longer than 30 days after last use.
Is there anything else I should know?
As states legalize marijuana, roadside testing for driver impairment due to marijuana use has become an urgent issue. This is a challenging testing problem because THC concentrations in the blood drop off quickly and the degree of impairment THC causes varies widely from person to person. That makes it very difficult to set a single legal level of THC in the blood, as is set with alcohol. While THC is currently the compound tested most often in blood to determine impairment, other cannabinoids are under investigation.
Some states, like Colorado, currently use blood testing and a cutoff concentration for THC in the absence of a better option. They are also piloting roadside oral fluid testing as a solution for determining impairment. However, there are still many obstacles to overcome before these tests are reliable.
Besides urine and saliva, what other types of samples may be used for marijuana testing?
Some laboratories offer marijuana testing on samples of blood and hair.
- A blood sample can be collected by inserting a needle into a vein and drawing blood into a tube.
- Hair may be tested and is usually collected from the crown of the head, although hair may also be collected from other parts of the body.
Newborns may undergo testing when the mother is known or suspected to have used drugs, such as marijuana, during the last trimester of pregnancy. In these cases, samples of meconium, a newborn's first bowel movement are typically collected by healthcare practitioners soon after babies are born. In recent years, umbilical cord tissue has gained more attention in drug testing after delivery instead of meconium as it can be collected immediately following birth.
Can THC screening detect if I’m using medical marijuana or a prescribed form of cannabis?
THC testing cannot distinguish between marijuana obtained via a medical card and marijuana obtained for recreational use.
Marijuana tests also cannot distinguish between THC from the cannabis plant and FDA-approved purified or synthetic prescription forms of THC.
Are the illicit synthetic forms of marijuana such as K2 and Spice the same thing as THC and can they be detected by marijuana testing?
The illicit synthetic cannabinoids such as K2 or Spice are not THC. These are mind-altering chemicals in liquid form that can be vaporized and inhaled using devices such as e-cigarettes or sprayed on to plant material so it can be smoked. The chemicals bind to the same brain receptors and may be marketed as synthetic THC or synthetic marijuana, but they are not the same substance. Illicit synthetic cannabinoids can have unpredictable and potentially life-threatening effects on the body, including seizures, brain swelling, and heart palpitations. Because these chemicals are not THC, they will not be detected with tests specific for THC or THC-COOH. A test that is specifically designed to detect the synthetic compound in K2 or Spice is needed. Even these tests don't necessarily detect all the synthetic cannabinoids that can be present in any given "spice" material.
Can I test positive from secondhand smoke?
Yes, though it is unlikely to occur at typical screening cutoffs. Research studies have shown that secondhand cannabis smoke can produce positive tests in non-smokers. However, it depended on the THC potency of the marijuana. Room ventilation also helped reduce THC exposure levels.
Can I be fired from my job for testing positive for marijuana in areas of the U.S. where it has been legalized?
Marijuana is legal for medicinal use in several states, and legal for recreational use in a fewer number of states plus Washington D.C. In these areas, U.S. federal employees and employees of federally-regulated industries are still prohibited from using marijuana and state law may not protect them from termination if they test positive for THC. State law may also not protect individuals whose private employers wish to fire them for using marijuana.
What can cause false-positive results in a marijuana test?
False positives have been reported for THC screening tests, which is why many positive screens are confirmed with a more specific test. The causes of false-positive screening results are not always able to be identified.
The chemical signatures of marijuana metabolites are unique and not likely to be mistaken for many other legal substances in a confirmation test. In older tests, ibuprofen could lead to false-positive screening results, but this is no longer the case.
The only substances that will cause a positive on confirmation tests are those that actually contain THC.
How long will a drug test detect THC after marijuana use?
Detection times for THC vary widely and depend on a number of factors. These include the dose of THC, frequency of use, an individual's metabolism and the type of sample tested. For example, THC can be detected in urine anywhere from 3 days to more than 30 days after use.
Why would collection of a urine sample need to be observed by a healthcare professional?
Some individuals attempting to evade drug testing will try to submit another person's urine sample or a commercial product as their own urine sample for testing. To prevent this practice of sample substitution, some legal entities may require that collection of the urine sample be observed by a healthcare practitioner or other professional.