<P> Under the typical 50 ng / mL cutoff for THC in the United States, an occasional or on - off user would be very unlikely to test positive beyond 3--4 days since the last use, and a chronic user would be unlikely to test positive much beyond 7 days . Using a more sensitive cutoff of 20 ng / mL (less common but still used by some labs), the most likely maximum times are 7 days and 21 days, respectively . In extraordinary circumstances of extended marijuana use, detection times of more than 30 days are possible in some individuals at the 20 ng / mL cutoff . </P> <P> However, one must remember that every individual is different, and detection times can vary due to metabolism or other factors . It also depends on whether actual THC or THC metabolites are being tested for, the latter having a much longer detection time than the former . THC (found in marijuana) may only be detectable in saliva / oral fluid for 2--24 hours in most cases . </P> <P> The main metabolite excreted in the urine is 11 - nor - delta9 - tetrahydrocannabinol - 9 - carboxylic acid (delta9 - THC - COOH). Most THC drug tests yields a positive result when the concentration of marijuana in urine exceeds 50 ng / mL . Urine Testing is an immunoassay based test on the principle of competitive binding . Drugs which may be present in the urine specimen compete against their respective drug conjugate for binding sites on their specific antibody . During testing, a urine specimen migrates upward by capillary action . A drug, if present in the urine specimen below its cut - off concentration, will not saturate the binding sites of its specific antibody . The antibody will then react with the drug - protein conjugate and a visible colored line will show up in the test line region of the specific drug strip . </P> <P> Cannabis use is included in the "10 - panel urine screen", as well as the "SAMHSA - 5", the five drugs tested for in standard NIDA approved drug tests . </P>

How many mg of thc to test positive