How Long Does Marijuana Stay In Your System? Blood, Urine, And Hair

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Medical News TodaySubscribeHow long can tests detect tetrahydrocannabinol (THC) in the body, and which factors influence detection?

Medically reviewed by Alex Nguyen, PharmD, RPh, CPh — Written by Zawn Villines — Updated on April 29, 2025

Detection windows
Failing a drug test
Factors that influence detection
How to get cannabis out of the body faster
Summary

Tetrahydrocannabinol (THC) is the chemical in cannabis that makes people feel “high.” Tests can detect THC in the body for several days or even weeks.

The length of time this chemical stays in the body or continues to show in a drug test depends on many factors, including a person’s body composition, cannabis use, and the test’s sensitivity.

Drugs such as alcohol may completely disappear from the body in just a few hours. In comparison, cannabis lingers much longer.

Drug tests can detect THC in urine, blood, and hair for many days after use, while saliva tests can only detect the chemical for a few hours. This is because of the way the body metabolizes THC. This article discusses these time frames.

Cannabis detection windows

CBD pharmacy sign — Christian Ouellet/Getty Images

Research on how long a test can detect cannabis shows a wide range of averages. The detection window can vary depending on a variety of factors, including a person’s overall cannabis use.

For someone smoking cannabis for the first time, tests may detect it for about 3 days.
In someone who smokes cannabis 3 or 4 times per week, the detection window is 5 to 7 days.
For people who smoke cannabis once per day or more, tests may detect it in their system for 30 days or longer.

Detection windows also depend on the kind of test a person undertakes. The most common test for cannabinoid detection is the urine drug screen. General estimates for various cannabis tests are as follows:

Urine tests: These tests can detect cannabis in the urine for approximately 1 to 30 days after use.
Saliva tests: Typically, cannabis is detectable in saliva for up to 24 hours. However, some evidence suggests an oral test can detect THC from a THC cigarette for up to 30 hours after use.
Hair tests: This type is the most sensitive test, detecting THC for up to 90 days after use. However, older research notes that these test the oil in the skin that transfers to hair, so they may occasionally show a false positive.
Sweat tests: Cannabis may be detectable in sweat for 7 to 14 days.
Blood tests: A blood test can only detect THC for a few hours.

How much do you have to smoke to fail a drug test?

Drug tests can detect relatively small quantities of THC, and the amount of THC in a given cannabis cigarette varies. However, little research has examined how much a person must smoke to fail a drug test.

Additionally, tests can detect THC for longer periods in individuals who use cannabis products more frequently. This is because chronic cannabis use will result in THC accumulating in fatty tissues, which will result in a slower elimination of metabolites.

A 2017 study reports on testing where hair samples from 136 cannabis users self-reporting heavy, light, or no use of cannabis. For the study, researchers cut hair into 1-centimeter sections to test for exposure up to 1 month prior.

Some 77% of heavy and 39% of light users produced positive tests. No non-users had positive test results, suggesting that false positives in hair tests are relatively rare.

Factors that influence detection

Numerous factors influence whether a test detects cannabis, including the following:

Test sensitivity

More sensitive tests can detect lower doses of cannabis. Tests include blood, urine, hair, and saliva.

THC dose

Cannabis drug tests look for THC, not cannabis. So the amount of THC that a person consumes is a significant factor.

The effects of THC are cumulative. This means that a person who smokes several times over several days has consumed a higher THC dose than someone who smokes once, so they are more likely to test positive.

The strength of each dose of THC also matters. Without sensitive laboratory equipment, a person cannot reliably determine the strength of their cannabis.

How “high” a person feels is also not a reliable measure because numerous factors other than THC dose can intensify or weaken this feeling.

Body fat

THC is a fat-soluble compound, which means that fat cells store cannabis. As such, people with higher body fat concentrations may metabolize cannabis more slowly than those with less body fat.

Hydration

Dehydration increases concentrations of THC in the body. While drinking lots of water is unlikely to affect a drug test significantly, severe dehydration might.

Exercise

Exercise will not significantly change the rate at which the body metabolizes THC. However, exercising before a drug test might.

An older study notes a slight increase in THC levels following exercise in people who regularly use cannabis. This may be due to exercise causing fat cells to release THC. As such, exercise right before a drug test may increase the likelihood of a positive test result.

Metabolism

For a drug test to be negative, the body must eliminate THC from the system as well as metabolic chemicals that have links to THC. People with faster metabolisms typically eliminate THC more quickly than those with slower metabolisms.

How to get cannabis out of the body faster

Ultimately, there is no definitive method to get cannabis out of the body faster.

Exercising and staying hydrated can help support the body’s metabolic processes, but these may not noticeably affect THC excretion.

Overall, there is no reliable way to speed up the metabolism and removal of THC. The most important factor is the time from the last exposure to the testing time.

Summary

There is no way to accurately predict how long it will take an individual to metabolize cannabis and eliminate it from their bodies. Home tests can help people test themselves for the presence of cannabis in their system.

For almost all individuals, cannabis should disappear or be very low in concentration within 30 days. For infrequent users, it may take 10 days or fewer for cannabis to leave the body.

Alcohol / Addiction / Illegal Drugs
Blood / Hematology
Medical Devices / Diagnostics
Marijuana / Cannabis / CBD

How we reviewed this article:

SourcesMedical News Today has strict sourcing guidelines and relies on peer-reviewed studies, academic research institutions, and medical journals and associations. We only use quality, credible sources to ensure content accuracy and integrity. You can learn more about how we ensure our content is accurate and current by reading our editorial policy.

Detection windows for drugs in oral fluid: Cannabinoids, stimulants, and opioids. (2019).https://aaafoundation.org/wp-content/uploads/2019/07/19-0297_AAAFTS_Oral-Fluid-Research-Brief_r2.pdf
Frequently asked questions about regarding drug screen results. (n.d.).https://www.childrenscourt.vic.gov.au/sites/default/files/2020-09/Frequently-asked-questions-regarding-drug-screen-results.pdf
Hadland, S E, et al. (2017). Objective testing – Urine and other drug tests.https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4920965/
Moosmann, B, et al. (2015). Finding cannabinoids in hair does not prove cannabis consumption.https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4595642/
Sheikh, NK, et al. (2023). Cannabinoids.https://www.ncbi.nlm.nih.gov/books/NBK556062/
Taylor, M, et al. (2016). Comparison of cannabinoids in hair with self-reported cannabis consumption in heavy, light and non-cannabis users.https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5396143/

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Medically reviewed by Alex Nguyen, PharmD, RPh, CPh — Written by Zawn Villines — Updated on April 29, 2025

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