Here is a short article I've edited. The information comes directly from a manufacturer of drug testing supplies, the info was meant to help those administering the test. One issue that gives such a wide variance is the use of two different detection levels.

After smoking or eating cannabis the THC is extensively metabolized before excretion. The presence of tetrahydrocannabinol acid or the cannabinoid metabolite in urine is an indication of marijuana use. The excretion half-life of cannabinoid metabolites in urine, range based on different factors such as: weight, age, BMI, etc.


THC (marijuana / cannabis) is one of the "NIDA 5" - the five drugs tested for in the standard NIDA approved drug test. THC is detectable in Urine for 48-72 hours after single use. Habitual or chronic use can be detected in urine for up to 10 weeks depending on quantity, duration, and frequency of use.

THC is rapidly absorbed by inhalation and the gastrointestinal tract. It is almost completely metabolized. The predominant metabolite is 9-carboxy-11-nor-delta-9-THC, which found in the plasma, feces, and urine along with other compounds. Very low concentrations of THC may be detected in urine during the initial several hours, but tetrahydrocannabinol persists in urine at a detectable concentration for many days after smoking.

The standard THC test is a one step rapid, qualitative immunoassay, a biochemical test that measures the level of a substance in a biological liquid, typically serum or urine, using the reaction of an antibody or antibodies to its antigen. The assay takes advantage of the specific binding of an antibody to its antigen for the detection of tetrahydrocannabinol compounds (11-nor-THC-9-Carboxylic Acid) in urine. The cutoff concentration for a positive result in an immunoassay test is 50 ng/ml as recommended by the Substance Abuse and Mental Health Services Administration (SAMHSA) and NIDA. The cutoff for GC-MS and DOT is 15 ng/ml.


In other words if you are a chronic smoker, do not use the experiences of a casual user to gauge you're detectability time. A chronic chronic user can count on up to 10 weeks. Whereas, someone who rarely smokes could be clear in a fraction of the time.