Window of detection

The window of detection is the length of time after exposure during which a substance or its metabolite can still be found by a particular type of test.

It depends on the test matrix, since blood, saliva, urine and hair each retain compounds for different periods, and on the substance, the amount, the frequency of use and the individual's metabolism and body composition. Urine windows for THC metabolites are longer than blood windows because THC-COOH is stored in fat and released gradually. Published ranges are broad for these reasons.

The figures that appear in reference tables describe populations, not individuals, and they cannot tell a specific person how a specific test will read on a specific day. A longer window means a test is more likely to reflect exposure in the past rather than the present, which is why urine results do not indicate impairment. For cannabinoid product users, the relevant window is the one for THC metabolites; no product can shorten it or guarantee a result inside it.