Another claim about cannabis is that impairment due to smoking it lasts many days after using it, since THC is stored in the fat cells, leading to a low-grade haze long after the primary high is gone. This myth is based primarily on anecdotal evidence and the known fact that urine drug tests remain positive for at least several days after using, and longer for regular users. The tests however measure non-psychoactive metabolites, not active THC. And the blood levels of THC generally fall well below the psychoactive threshold within 2–4 hours of smoking (4–8 hours after oral use). A cannabis equivalent of a hangover may occur the morning after taking high doses, but even that ends much sooner than the legend suggests. Although smoking cannabis on a Friday night would most likely test positive in a urinalysis Monday, no amount of the psychoactive effect would be retained by that time.