"Recent scientific literature indicates that it is uncommon for occasional marijuana smokers to test positive for cannabinoid [metabolites] in urine for longer than seven days" at 20 ng/ml or above on the EMIT (Enzyme Multiplied Immunoassay Technique) test, the author concludes. "Following smoking cessation, chronic smokers would not be expected to remain positive for longer than 21 days, even when using the 20 ng/ml cannabinoid cutoff."

When tested at the 50 ng/ml cutoff threshold, infrequent users typically test negative for the presence of marijuana metabolites within 3-4 days, while heavy users typically test negative by ten days after ceasing use, the study found.

While several clinical trials from the 1980's found cannabis metabolites to be identifiable in the urine at low concentrations for longer periods of time, particularly in heavy users, the author suggests that more advanced drug-testing technology has narrowed this window of detection.

"As cannabinoid screening tests evolved, these improved assays became more selective in the manner in which they detected marijuana metabolites," the author writes. "As detection specificity increased, the length of time cannabinoids were being detected in urine decreased. ... Therefore, the results of cannabinoid elimination investigations performed in the 1980's may no longer be applicable to estimating the detection window for marijuana in urine using todayΉs testing methodologies."

After reviewing data from more recent clinical investigations of chronic marijuana smokers, the author reports that the "average detection window for cannabinoids in urine at the lowest cutoff concentration of 20 ng/ml was just 14 days." However, the author also notes that a minority of subjects continue to test positive for cannabis metabolites after 28 days, even when tested by more advanced drug-testing technology.

Approximately 55 million drug screens are performed annually in the United States. The majority of these are workplace urinalysis tests, which detect the presence of drug metabolites (inert byproducts produced after a substance is metabolized by the body), but not the substance itself. Consequently, the US Department of Justice affirms that a positive drug test result for the presence of a drug metabolite "does not indicate ... recency, frequency, or amount of use; or impairment."

For more information, please contact Paul Armentano, NORML Senior Policy Analyst, at (202) 483-5500. Full text of the study, "The marijuana detection window: Determining the length of time cannabinoids will remain detectable in urine following smoking," is available online at: http://www.ncdi.org/ndcirpub.html