Bologna, Italy: Subjects exposed to second-hand cannabis smoke, even for brief periods, can test positive for THC on a hair follicle test, according to data published in the journal Forensic Science International.
A team of Italian investigators assessed the ability of hair tests to detect THC in subjects exposed to side-stream cannabis smoke. Study participants were exposed to second-hand smoke from a single marijuana cigarette for 15 minutes in a non-ventilated environment.
Subjects’ hair samples tested positive for THC following passive exposure, with male subjects possessing higher THC values than women. All subjects tested negative for THC metabolites in their urine.
“Our study showed that hair contamination could arise in vivo even after short single exposures to cannabis, … underlining the need for a careful interpretation of results of hair analysis in forensic toxicology,” the study’s authors concluded.
NORML has consistently criticized the use of drug detection tests, such as blood testing, oral fluid tests, urinalysis, and hair testing, in the workplace and elsewhere because they cannot accurately determine behavioral impairment or recent drug ingestion.
Full text of the study, “Analysis of delta-9-tetrahydrocannabinol and cannabidiol on hair after single and repeated short in vivo passive exposures to low- and high-delta-9-THC cannabis,” appears in Forensic Science International.