How long is cannabis active half life after smoking?

The cited half-life is 10 hours to 20 days. This drug attaches to fat cells in the body which slows its loss from the body. A single brief use may not be detectable in a few days. Use of a highly concentrated amount or by a chronic user can remain detectable for a month or more in urine or blood. Locations that test hair can detect ant exposure during the hair growth period.

Wide range as it also depends on the type of metabolite being measured as well as the individual liver enzymes make up and speed of processing it. From 1 day to couple of weeks or even more for occasional users to chronic users is to be expected for inhaled THC’ s half life.