[Know your rights]

"The positive results of a urine screen cannot be used to prove intoxication or impaired performance. Inert drug metabolites may appear in urine for several days, even weeks (depending on the drug), without being related impairment." - Walsh & Hawks, Employee Drug Screening, National Institute on Drug Abuse (NIDA), at 4 (1986).

[DBrow]

The residual metabolites came up because I Clustr'd up a bunch of articles mentioning cannabis withdrawal, and the slow elution of these metabolites were offered as an explanation. Perhaps the metabolites do not contribute the same effects as Delta-9 THC, but are biologically active in other ways.

No flames, please, about cannabis withdrawal; I'm just the messenger. I think the issue is irrelevant to the topic of the thread.

The long-halflife metabolites are used just forensically; they can prove that you were exposed to cannabis at some time in the past (like going to a concert and getting secondhand smoke that costs you your job).