Urine test results for detecting marijuana depend on many factors, including frequency of use. The marijuana metabolite THC-COOH builds up to a high level in regular users (more than once a week), often on the order of hundreds of nanograms per milliliter (ng/ml), from which it may take weeks to decline back below the threshold of detection. The situation is different for occasional marijuana users (no more than once a week), who often clear up in a couple of days.
The following figure illustrates typical urine testing profiles for “one-time” marijuana users, who are subjects who were clean before going for tests. The same goes for occasional users who indulge a couple of times per month.
In the above image, subjects B and G illustrate typical “one-time” responses in a group of study subjects and they received a dose of one standard NIDA cigarette. These subjects were monitored for urine levels of marijuana metabolite (THC-COOH) at regular intervals after smoking marijuana. Both the subjects were positive at the standard cutoff threshold of 50 ng/ml, which is the standard in most government-required testing programs for up to two days after smoking.
The urine levels of metabolite fluctuate throughout the day. In the case of subject G, the level fell beneath the 50 ng threshold around 24 hours after smoking, but soon rebounded above it. In short, it is possible to flunk a drug test despite having passed one a while earlier.
Subject “E” was termed as an exceptional subject who never exceeded 50 ng/ml despite having smoked the same dose as other study subjects that illustrates the high degree of individual variation in urine testing.