The Scientific Basics of THC and THC COOH (carboxy THC)
This article was originally published by Colorado NORML Board Member Emeritus Lenny Frieling on his website. Reprinted with permission.
An example of useless information for determining marijuana-caused impairment is looking at urine in a lab. Urine is cheap and easy to test for the amount of one metabolite of THC. A metabolite is, simply put, a chemical produced by the body from another chemical taken into the body.
For our purposes, we're looking at one of the hundred or so cannabinoids found in pot, delta-9 THC, being introduced into the body. That is the primary cannabinoid which gets us "stoned." That is referred to as being "psychoactive." The metabolite found in urine is inactive, having NO psychoactive effect. It is written THC COOH and read "carboxy THC." It does not get anyone stoned. BUT, the metabolite is the chemical that may be found for weeks if not months after intake of the marijuana.
Being lipid (fat) soluble and not water-soluble (most medication is water-soluble) it is stored in the fat cells of the body for quite long after any impairing impact of the active THC remains. It may be found weeks or longer after the intake of marijuana, while the impairing effect of the active delta-9 THC may be almost gone within three hours more or less.
The level of the inactive cannabinoid THC COOH, found in blood or urine, reveals nothing about current impairment, and nothing about the time or amount of consumption. Contrary to the belief of some "experts" and of some prosecutors, the ratio of THC COOH to active THC also means nothing.
Since the metabolic process of the body converting (metabolizing) active THC into inactive carboxy COOH THC takes some hours, the presence of the inactive metabolite is arguably exculpatory, (showing a lack of guilt) because it indicates that the consumption was possibly not recent but was at least hours before the sample, blood or urine, was collected. The impairing effect of active THC appears to be most pronounced from about 1 1/2 hour to three or 4 hours after intake. This does NOT correspond to the blood level of active THC. The level in blood reaches a maximum almost immediately, and just as quickly drops in blood. This delay between blood level and impairment is described as "counterclockwise hysteresis." It is noteworthy that mixing alcohol with marijuana causes impairment which is greater than would be expected from the blood levels.