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. These include:
- how much body fat a person has
- how much and how often they consume the drug
- the sensitivity of the drug test
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 THC for a few hours. This is because of the way the body metabolizes THC.
THC is a lipid-soluble chemical. This means that it binds to fat in the body, which increases the length of time it takes for someone to eliminate THC.
Cannabis Detection Windows
Research on how long a test can detect cannabis shows a wide range of averages. Research from 2017 estimates a detection window for a single cannabis cigarette of about 3 days.
The same study emphasizes that detection windows vary and depend on how often a person smokes. It showed:
- 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 5–7 days.
- For people who smoke cannabis once a 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 1–30 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. Some saliva tests may also detect cannabis from oral dosing, such as brownies, Sativex, Marinol, for up to 44 hours.
- 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 skin that transfers to hair, so they may occasionally show a false positive. A person who comes into contact with a THC user could, theoretically, test positive on a hair test.
- Sweat tests: Cannabis may be detectable in sweat for 7–14 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 a month prior.
Some 77% of heavy users 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.
How long can you detect Marijuana in the body?