A recently released study finds exposure to “second-hand” cannabis smoke can result in detectable levels of cannabinoids in hair, complicating forensic hair analysis interpretation.
Hair follicle drug tests can detect cannabis use over an extended period, typically up to 90 days, depending on the length of the hair sample analyzed. This type of testing is sometimes used for employment, legal, or medical purposes. But hair follicle tests aren’t 100% accurate and cannot determine the exact date of drug use as hair growth rates vary.
Researchers from Italy’s University of Bologna set out to assess whether detectable hair levels of delta-9 tetrahydrocannabinol (Δ9-THC) and cannabidiol CBD could occur from short, single and repeated passive exposure to cannabis and “light cannabis” (low in THC, high in CBD) smoke – and whether the two products could be distinguished.
Several volunteers were subjected to weekly 15-minute exposures to low-Δ9-THC (0.5 %) cannabis smoke over a month that was delivered by a pump inside a car. After a 1 month washout period (when participants weren’t exposed), exposures were repeated under the same conditions with high-Δ9-THC (5 %). Hair and urine samples were collected after each exposure.
While the urine tests always proved negative, hair samples were positive for CBD after exposure to “light cannabis”, and for THC after exposure to high-Δ9-THC cannabis, with levels also typical of drug use.
The researchers concluded:
“Our study showed that hair contamination could arise in vivo even after short single exposures to cannabis and “light cannabis”, underlining the need for a careful interpretation of results of hair analysis in forensic toxicology.”
“In vivo” refers to in the living body of a plant or animal.
The study has been published in the journal Forensic Science International. It follows an in vitro (in an artificial environment) study from last year by some of the same researchers that concluded hair analysis might allow testing to determine whether external contamination by products containing low or high Δ9-THC, but not the delivering mode.
Commenting on the latest research, the USA’s National Organization for the Reform of Marijuana Laws (NORML) said:
“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.”
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