How Long Does Marijuana, Weed, Pot (THC) Stay In Your System?

The half life of THC depends on potency, frequency of use and mode of administration. But generally, the THC found in marijuana can stay in the body for days or weeks after use. More on how long THC stays in the system here.

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Reviewed by: Dr. Dili Gonzalez, M.D.

ARTICLE OVERVIEW: The detection window for marijuana and THC depends on quantity, potency, frequency of ingestion, personal metabolism, the amount of fat in the body and the drug testing method used. Details below.


How Do You Take Marijuana?

In 2016, an estimated 24 million Americans aged 12 and older reported current use of marijuana. [1]Most people take marijuana by smoking or eating it.

Marijuana contains tetrahydrocannabinol, or THC for short. THC is a chemical that causes psychoactive effects by binding to cannabinoid receptors in the brain. In other words, THC is the chemical that gets you high. THC is found in the following products:

  • Dronabinol, a synthetic form of marijuana
  • Hash, resin from the hemp plant cannabis sativa
  • Hashish oil
  • Marijuana buds
  • Marijuana flowers
  • Marijuana leaves

People smoke marijuana in hand-rolled cigarettes called joints or in pipes or water pipes called bongs. They also smoke it in blunts, emptied cigars that have been partly or completely refilled with marijuana. To avoid inhaling smoke, other people have started using vaporizers. These devices pull the active ingredients from the marijuana or liquid extract and collect vapor in a storage unit. So, instead of smoking, a person then inhales the vapor.

People can also mix marijuana in food and edibles, such as brownies, cookies, or candy, or brew it as a tea. A newly popular method of use is smoking or eating different forms of THC-rich resins.

Main Uses

Apart from getting high, there are legitimate reasons why people use marijuana.Even though it´s a Schedule I drug and is classified as having no medical use by the federal government [2],people have used marijuana, its individual components, or similar synthetic substances for a variety of health conditions for at least 3,000 years. [3]

In January 2017, the National Academies of Sciences, Engineering, and Medicine published a report that summarizes the current evidence on both therapeutic effects and harmful effects. [4] The report concludes that the effects of cannabinoids are modest for the following conditions:

1. In adults with chemotherapy-induced nausea and vomiting, oral cannabinoids are effective antiemetics.

2. In adults with chronic pain, patients who were treated with cannabis or cannabinoids are more likely to experience a clinically significant reduction in pain symptoms.

3. In adults with multiple sclerosis-related spasticity, short-term use of oral cannabinoids improves patient reported spasticity symptoms.

Further, the FDA has approved THC-based medications, prescribed in pill form for the treatment of nausea in patients undergoing chemotherapy, and to stimulate appetite in patients with wasting syndrome due to AIDS. It was also approved a CBD-based liquid medication called for the treatment of two forms of severe childhood epilepsy, Dravet syndrome and Lennox-Gastaut syndrome. [5]

Peak Levels

On average, the effects of marijuana last between 3 – 4 hours. However, peak levels of THC depend on how it enters the body. When cannabis is ingested by mouth, THC levels peak after 1 to 6 hours.When inhaled, THC is rapidly absorbed into the bloodstream with a peak concentration in 2 to 10 minutes.

Half Life

The half life of a drug is the amount of time it takes for measured amounts in the bloodstream or urine to decrease by half. The half life for THC is long because THC is stored in the body’s fat cells. This is because THC is highly lipid and not easily dissolved in water. Therefore, the blood plasma and urinary half-life of THC are best estimated at 3 – 4 days after ingestion. However, this half-life can be even longer depending on the quantity of THC ingested and frequency of use. The half-life for marijuana may even extend to 10-12 days after ingestion.

Marijuana Detection Windows

Because THC is a highly fat-soluble compound, it can build up a very long half-life for elimination among heavy users. In the case of people who smoke once per week, THC levels increase in their bodies over time because THC has never been fully eliminated. So, regular users of marijuana must realize that THC is generally more detectable in their systems than in the bodies of periodic or episodic users of marijuana.

Furthermore, detection windows for weed will be based also on a person’s metabolism and fat content in the body. Finally, the detection window for THC depends on quantity, potency, duration of use, frequency of ingestion, and the method used to detect THC or its metabolites.

Generally, marijuana detection windows for biological samples are as follows.

Blood: 3 days to 2 weeks.

Hair: 90 days.

Saliva: 1 day.

Sweat: 7 to 14 days.

Urine: 1 to 30 days.

Marijuana Drug Testing

Marijuana can be detected in urine, blood, hair and saliva drug tests. The most common drug test for marijuana is a urine based test.These different types of drug tests employ various methods with different sensibility and specificity,and include methods such as:

  • Enzyme immunoassay
  • Gas chromatography
  • High pressure liquid chromatography
  • Radio immunoassay
  • Thin layer chromatography

Each type of drug test isused for specific situations and depends on there as on for the test. Let’stake a deeper look at each of these screening methods, and their general detection windows.

Blood Tests for Marijuana

Blood testing typically detects marijuana use that occurred within 2 to 12 hours of the test.Drug testing of blood samples is usually only performed in emergency situations. This is because taking blood is considered “invasive” and unnecessary unless acute use needs to be recorded in cases of car accidents or injury.

Hair Tests for Marijuana

Hair testing for marijuana can detect substance use over the period of days to months, and, in some cases, years after use. Conversely, hair testing is not helpful in detecting sporadic use when weekly or monthly testing is required as part of a drug treatment plan.

Because of the long period of detection for hair samples, this type of drug test is useful for detecting chronic substance use, understanding the duration of a patient’s drug use over the long term, and indicating periods of abstinence. So, hair tests may be ordered by courts or doctors to view patterns of use over time.

Saliva Tests for Marijuana

Oral fluid testing can detect marijuana for up to 24 hours after use. This method is less commonly used but oral samples represent a convenient, promising matrix for many settings. Unlike urine samples, oral samples are not easily tampered with, and can be collected with minimal invasion of privacy.

Urine Tests for Marijuana

The most commonly used urine drug testing for pot involves an automated immunoassay either alone as a point-of-care test. The cutoff value for the test is 50ng/mL… or samples are submitted as an initial screen for a 2-step testing procedure followed by a confirmatory test with a cutoff value of 15ng/mL.[6] Its collection is somewhat invasive since it requires either a sophisticated collection protocol which is not readily available in medical offices or direct observation by a clinician or a relative to prevent tampering.

What If I Test Positive…

In most cases, if you test positive you´ll still have chance to retake the test with the same or a different biological sample.It´s important to know every state and municipality has different rules regarding workplace, clinical and student drug tests. Here are some of the common consequences and what you can do about them.


Here are some possible scenarios:

  • An employer may refuse to hire you.
  • An employer could restrict your promotion or terminate your contract.
  • An employer may allow you a chance for rehab, and a return under some conditions.
  • Your unemployment benefits could be denied.

If you test positive for marijuana in a workplace test, you can claim the results are mistaken or wrong. Cross reactivity ad false positive tests are possible (see below). Here are some measures to prove the test is wrong:

  • Ask your employer if it is possible to retake the test.
  • You can require the laboratory to test your sample again.
  • Your employer can require an additional test with only one-hour notice.
  • You can ask for a hair drug tests to be done, although you may have to cover the costs.


Here are some possible situations:

  • Your doctor can cut you off your medications or dismiss you as a patient.
  • You could be excluded from a competitive sport.
  • You could be visited by social services.
  • You may be facing time in jail, or state or federal prison, OR lose your privileges in a probation setting.

If you feel that, your test result is incorrect and that you haven’t smoked or used marijuana you can:

  • Talk with your practitioner about any medications you are using.
  • Ask for a laboratory confirmatory test that is more specific.
  • Participate in another screening and assessment performed by your doctor or another medical professional.


The worst-case scenarios might be:

  • It may affects your college loans.
  • You may have a criminal record.
  • You could spend time in jail, or state or federal prison.
  • You might not be able to join the military.

The primary purpose of studentdrug testing is not to punish students who use illicit drugs but to prevent future illicit drug use. Therefore, most schools will first tell your parents about the result. Depending on levels of possible addiction, counseling or rehab can be considered.

False Positive

False positive results are associated with the use legal medications like Marinol and proton pump inhibitors. [7] A false positive test for marijuana can also occur also after you’ve been exposed secondhand marijuana smoke or after consuming hemp derived products.Additionally, you may trigger a false positive drug test for marijuana if the testing method is an immunoassay for multiple drugs. Compounds in the biologic specimen other than the actual substance or its metabolite bind to the assay and trigger a false positive result.

Home Tests

Most home tests for marijuana are urine test kits that use immunoassays, or IAs. Although IAs have high sensitivity to THC, these tests often displace poorer specificity owing to cross-reactivity. This is why home tests give us a qualitative result that should be confirmed with a more specific test.

Why does cross-reactivity occur? The most commonly used immunoassays in home drug testing kits include simultaneous testing for other drugs. This can include amphetamines, cocaine metabolites, and opiates. But during testing, compounds in the biologic specimen other than the actual substance or its metabolite bind to the assay and trigger a false positive result.

Marijuana Addiction Liability

Marijuana use can lead to the development of a substance use disorder, also called addiction. Addiction is a medical illness in which the person is unable to stop using marijuana even though it’s causing health and social problems in their life

Research suggests that between 9 and 30 percent of those who use marijuana may develop some degree of marijuana use disorder. People who begin using marijuana before age 18 are four to seven times more likely than adults to develop marijuana use disorder.

Many people who use marijuana long term and are trying to quit report mild withdrawal symptoms that make quitting difficult. These include:

  • Anxiety
  • Cravings
  • Decreased appetite
  • Grouchiness
  • Sleeplessness

Problems With Marijuana? Get Help Now!

You will know if you are addicted to marijuana if you experience withdrawal symptoms when you quit taking it… and if you begin to crave marijuana when you don’t have access to it.

Compared to those who don’t use marijuana, those who frequently use large amounts report the following:

  • Higher likelihood of dropping out of school.
  • Less academic and career success.
  • Lower life satisfaction.
  • More accidents and injuries.
  • More job absences.
  • More relationship problems.
  • Poorer mental and physical health.

There is help for people who are addicted to marijuana, but it is only useful when you are ready to stop. Treatment generally includes some form of psychotherapy combined with support groups. And it can help to get out of your environment to focus on yourself.

Give us a call to learn more about treatment.

We know addiction.

Compassionate support staff are waiting to talk to you about your options.

Let’s verify your coverage for treatment at an American Addiction Centers location. Your information is kept 100% confidential.


More Questions?

Do you still have questions about how long THC will stay in your system after marijuana consumption?Please leave us your questions or comments here. We will take the time to try to answer all of your questions with a personal reply ASAP.

[1] SAMHSA: 2016 NSDUH statistics on marijuana use
[2] DEA: Drug Scheduling
[3] NCCIH: Marijuana and Cannabis
[4] National Academies: The Health Effects of Cannabis and Cannabinoids, The Current State of Evidence and Recommendations for Research
[5] NIDA: Is Marijuana a Safe and Effective Medicine?
[6] NCBI:Objective testing – Urine and other drug tests
[7] Research Gate: False Positives in the Detection of Drugs
NCBI:Interpretation of workplace tests for Cannabinoids
NCBI: Medicinal cannabis: History, pharmacology, and implications for the acute care setting
About the author
Lee Weber is a published author, medical writer, and woman in long-term recovery from addiction. Her latest book, The Definitive Guide to Addiction Interventions is set to reach university bookstores in early 2019.
Medical Reviewers
Dr. Dili Gonzalez, M.D. is a general surgeon practicing women's focused medici...

All of the information on this page has been reviewed and verified by a licensed medical professional.

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