A. To answer this question, we must look at it from two key issues it presents. We will address each separately.

Issue 1. What is the time frame of likely positive urine cannabinoids test results (assuming a standard 50 ng/mL immunoassay cut-off) after cessation of documented chronic cannabis use?
Our review of the literature leads us to the conclusion that documented chronic users may stay positive (using current urine cannabinoids immunoassays at a 50 ng/mL cut-off) for 2-3 weeks after claimed last use, unlikely longer. A maximum of one month would certainly be a conservative time frame, except in highly unusual circumstances. Of course, this does not mean that every claimed chronic user should automatically be given a one month allowance before positive test results are judged as renewed use. A close review (i.e. quantitative levels, time frame after claimed last use, sequence) of any positive test results occurring before one month after claimed last use may demonstrate that they are not consistent with residual cannabinoids from prior chronic use but rather represent renewed use. Controlling for specimen dilution through creatinine and/or specific gravity measurements are important and highly useful in making such assessments. It has also been proposed that if the quantitative level of cannabinoids (after controlling for specimen dilution) in any subsequent positive test result increases by more than 50% from some prior test result it is convincing evidence of renewed use.

Issue 2. What is the time frame of likely positive results after acute one-time cannabis use? After cannabinoids have been effectively cleared from the system (not simply "negative" but with test results consistent with a drug-free control), then a subsequent one-time use of cannabis would likely lead to positive urine test results (again when using current urine cannabinoids immunoassays at a 50 ng/mL cut-off) for only 1-2 days, unlikely longer.