Marijuana and Impairment —By Richard Bayer, MD

The Journal of Cannabis in Clinical Practice

Autumn 2005


«Since THC acts identically whether synthetic or herbal, we should look at the warnings section of the US Food and Drug Administration (FDA)-approved dronabinol (synthetic THC marketed as Marinol): “WARNINGS: Patients receiving treatment with Marinol should be specifically warned not to drive, operate machinery, or engage in any hazardous activity until it is established that they are able to tolerate the drug and perform such task safely.” This is sound advice. […]

Since synthetic THC and herbal THC are identical once inside the body, there is no scientific rationale for discrimination against those who prefer medical THC from an herbal rather than a synthetic source. The Marinol package insert warnings should be heeded regardless of whether a person uses synthetic FDA-approved THC (as in Marinol) or herbal THC (as in marijuana or cannabis). […]

Things like non-prescription over-the-counter medicines, acute influenza, or a family emergency resulting in lost sleep can cause impairment. […]

Urine drug testing to monitor therapy is not routinely used in clinical medicine. It is helpful in toxicology or poisoning cases when a doctor is uncertain what drugs are in the body. Urine tests are also used in medical-legal settings. The standard urine test for “marijuana” does not test for the “parent drug,” THC, but tests for an inactive non-psychoactive metabolite or breakdown product of THC.

Inactive breakdown products in a standard “urine marijuana test” can remain positive for weeks to months after consuming cannabis, even when there is no impairment. The US Department of Transportation commented about urine drug testing that, “while a positive urine test is solid proof of drug use within the last few days, it cannot be used by itself to prove behavioral impairment during a focal event.” In other words, urine drug testing does not prove impairment, it only proves recent use. […]

Recent studies continue to show that “no increased risk for road trauma was found for drivers exposed to cannabis.” […]

Daily cannabis users (like patients) can have levels as high as 6 to 10 ng/ml without clinical impairment even after 24 or more hours of abstinence.»