Infrequent Pot Use Often Goes Undetected On Hair Strand Tests

Baltimore, MD: Drug testing technology that detects the residual presence of cannabinoids and/or their metabolites in the hair typically fails to identify occasional marijuana users, according to trial data published online (ahead of print) by the journal Forensic Science International.

Thirty-eight males with a documented history of marijuana use participated in the trial. Among those participants who used marijuana daily, 85 percent tested positive for either THC or THC metabolites in the hair. By contrast, among those participants who smoked cannabis occasionally (defined as one to five marijuana cigarettes per week), only 52 percent tested positive for pot.

Investigators also reported that subjects administered oral THC during the course of the trial did not test positive for cannabinoid metabolites in the hair.

Authors reported no difference in cannabis detection rates between Caucasian and African American subjects. Previous studies of hair testing technology have suggested that certain drug concentrations, particularly cocaine, are more detectable in darker hair colors.

Hair strand testing typically detects the presence of drug metabolites that have passively diffused from the blood stream to the base of the hair follicle. Proponents of the testing technology argue that it allows for a longer window of drug detection than saliva testing or urinalysis.

For more information, please contact Paul Armentano, NORML Senior Policy Analyst, at (202) 483-5500. Full text of the study, “Cannabinoid concentrations in hair from documented cannabis users,” appears online on the Forensic Science International website.