How Long Does Marijuana Stay in Your System?

Person smoking a marijuana blunt

With marijuana becoming decriminalized in many states, the topic of drug testing has become more important than ever. Marijuana, also known as weed or pot, seems to have fallen into a grey area where some employers continue to drug test for it and others have stopped.

The plant marijuana, or cannabis, contains dozens to hundreds of active chemicals with different effects in the body. Currently, research around this plant falls behind where it should be. With its increasing legality throughout the U.S., however, we are beginning to learn more about the pharmacology of cannabis. Medical research can now proceed in directions that it could not before.

Marijuana contains unique chemicals called cannabinoids. This chemical category affects a cellular pathway in the body called the endocannabinoid system.

When it comes to drug testing, the primary topic of discussion revolves around tetrahydrocannabinol (THC). THC is the molecule that causes intoxication, euphoria, relaxation and changes to sensory perception. THC can stay in the body for several days and even weeks, long after it has stopped producing the intended effects.

Duration of Effects of Marijuana

How long do the effects of marijuana last? A person will feel the effects of weed for about one to three hours when smoked.

Ingesting it in food or drinks can produce effects that last much longer, sometimes eight hours or more. Marijuana taken by mouth releases slowly in the stomach and intestines, prolonging the effect beyond what smoking can do.

THC Half-Life

The half-life of marijuana varies based on frequency of use. People who use pot infrequently can expect a half-life of about 1.3 days. The half-life for frequent users is between five and 13 days.

A half-life is how long the body takes to metabolize half the amount of an ingested drug. For example, an infrequent user who takes 10 mg on Monday will have 5 mg left at the end of Tuesday and 2.5 mg still in their blood on Wednesday. A frequent user will have 5 mg in their blood by Friday and possibly into the following week.

Based on the half-life, an infrequent user will clear THC completely in about seven days. A frequent user can take up to 65 days.

Marijuana Detection Times

Weed detection times vary based on what kind of test is being used. Drug screens can be performed using urine, saliva or hair. The detection window runs from a few days to several weeks, but some tests can detect it for months.

So, how long does marijuana stay in your urine, blood, saliva and hair?


Marijuana urine detection time is about 15 days after last use for frequent users. People using weed less frequently can expect detection for up to five days.

Urine drug screens are cheap, easy and noninvasive. Most employers will prefer this type of drug screen over more expensive options.


If THC is found in the blood, it means the person is currently intoxicated. Therefore, this test is not a common screening method due to its narrow detection window. Marijuana blood test detection time is about 48 hours after last use.


A marijuana saliva test can detect THC for up to 24 hours. The small detective window makes saliva testing a poor option.


Marijuana hair tests can measure THC for up to 90 days. A hair test is unique because the detection window depends on the growth speed of hair, not how quickly the body metabolizes the drug. When THC is present in the bloodstream, it deposits into hair follicles. Deposited THC stays locked in the hair forever, only leaving the hair when the hair is cut off.

Factors Affecting How Long Marijuana Stays in Your System

THC metabolism is very complex, but we know a few key characteristics that help understand THC in the body.

  • Amount used: Higher usage makes THC accumulate in the body. Since the body can only metabolize so much THC at a time, accumulation slows down metabolism.
  • Frequency of use: THC accumulates in people using it frequently or for long periods. Accumulated THC has a longer half-life than short-term usage, and the body takes more time to remove it.
  • Metabolism rate: Marijuana and metabolism are mostly linked by usage. Among heavy users, the half-life of marijuana ranges from five to 13 days. In this group of people, THC can be removed from the body in one month, but it may take up to two months.
  • Body fat percentage: THC is lipophilic, meaning it is soluble in fat solutions but not water solutions. People with a higher body fat percentage may metabolize pot more slowly than others.

False Positives for Marijuana

Some drug screens will return with a positive result even when the person has not been using pot or substances that contain THC. If a substance that is not THC triggers a positive result, this is called a false positive.

Any test has the potential for a false positive, but research has confirmed a few factors that most certainly impact urine drug screens.

Most marijuana false positives are caused by other drugs. Substances that trigger a false positive for urine drug screens include:

  • Hemp foods
  • Over-the-counter pain medications (ibuprofen, naproxen)
  • Pantoprazole (for acid reflux)
  • Sustiva (efavirenz) and HIV medication

When a drug test comes back positive, the person will be asked about what other medications they take to rule out false positives. The urine sample is then sent to another lab for a test called gas chromatography-mass spectrometry (GC-MS). GC-MS can confirm the sample with almost 100% accuracy, so a false positive drug screen must be confirmed with this type of test.

How the Body Processes Marijuana

How is weed processed in the body and how does the body process THC? THC and other cannabinoids are broken down by the liver

Liver cells make small proteins called enzymes that change the shape of the molecule. Research has revealed 100s of different metabolites of THC, meaning the body has many pathways for removing the drug. A metabolite is a product the body forms after metabolizing THC.

Drug tests are not easy to beat, and the best way to test positive for marijuana is to be drug-free. If you or a loved one is ready to stop using weed, The Recovery Village Ridgefield is here to help. Contact us today to learn more about treatment plans that can work well for you.

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Moeller, Karen E., et al. “Urine Drug Screening: Practical Guide for Clinicians.” Mayo Clinic Proceedings, January 2008. Accessed July 21, 2019.

National Institute on Drug Abuse. “What Are Marijuana Effects?” 2019. Accessed July 21, 2019.

Oberbarnscheidt, Thersilla; Miller, Norman. “Pharmacology of Marijuana.” Journal of Addiction Research & Therapy, 2017. Accessed July 21, 2019.

Westin, Andreas; et al. “Can Physical Exercise or Food Deprivation Cause Release of Fat-Stored Cannabinoids?” Basic & Clinical Pharmacology & Toxicology, April 22, 2014. Accessed July 21, 2019.

Medical Disclaimer: The Recovery Village aims to improve the quality of life for people struggling with a substance use or mental health disorder with fact-based content about the nature of behavioral health conditions, treatment options and their related outcomes. We publish material that is researched, cited, edited and reviewed by licensed medical professionals. The information we provide is not intended to be a substitute for professional medical advice, diagnosis or treatment. It should not be used in place of the advice of your physician or other qualified healthcare provider.