Many people wonder how long marijuana remains in the system after it is used. Especially in the case of drug tests, there are numerous factors that must be evaluated to determine if a subject is indeed free of marijuana.
It is key to keep in mind that even if a person is no longer high from marijuana use, the drug is still present in his or her body. THC, the active ingredient in cannabis, is what stays behind in a user’s system even after the high is gone. Drug tests meant to detect marijuana are actually looking for the presence of THC in the subject’s spit, urine, hair, or blood. Each of these body parts will maintain the presence of THC for a unique period of time.
Spit, for example, does not register marijuana use instantly. It takes about an hour after use for THC in saliva to register on a drug test. After about 12 hours, however, THC will have begun to leave a marijuana user’s saliva, thus decreasing the effectiveness of a saliva-based drug test.
THC can be detected with urine tests for varying periods of time based upon the frequency of a subject’s marijuana use and how much of the drug he or she smoked at a given time. Urine tests can register the presence of THC for 45 days in heavy users; 7 to 30 days is the general timeframe for lighter marijuana smokers. THC will generally be present in the systems of daily marijuana users for at least three weeks. Even if a person has only smoked marijuana a single time, urine tests can register THC for up to a week after use. It takes 2 to 5 hours after use for a urine test to register THC.
Long after THC is undetectable in a subject’s spit or urine, it can remain present in the hair follicles. Almost instantly after marijuana is inhaled, it enters the bloodstream. Because blood is necessary for hair to grow, it must enter the roots of each strand; if THC is present in the blood, it will grow with the hair, remaining in the strand. It usually takes only about a week for a strand of hair to grow to the proper length that it can be tested for THC. THC, and most other drugs, will remain detectable in hair for an extremely long time, but most labs will only test for drug use within the past 90 days without a court order to test for a longer period of time.
Thus, without referring to a particular part of the body, there is no generalized answer for the length of time marijuana can be detected in the body.