Analysis of Δ9-tetrahydrocannabinol (Δ9-THC) and cannabidiol (CBD) on hair after single and repeated short in vivo passive exposures to low- and high-Δ9-THC-cannabis.

Prolonged cannabis smoke exposure could give rise to detectable levels of cannabinoids in hair, complicating forensic hair analysis interpretation. Exposure to "light cannabis", i.e., products that are low in Δ9-tetrahydrocannabinol (Δ9-THC) and enriched in cannabidiol (CBD), can additionally lead to contamination, as shown in vitro. The aim of the present study was to assess whether detectable hair levels of Δ9-THC and CBD could arise in vivo from short, single and repeated passive exposure to cannabis and "light cannabis" and whether the two products could be distinguished. Four volunteers underwent weekly 15-minute exposures to low-Δ9-THC (0.5 %) cannabis smoke, delivered by a pump inside a car, over a month. After 1 month of washout, exposures were repeated with the same scheme with high-Δ9-THC (5 %). Hair and urines samples were collected after each exposure. Hair samples were tested, with and without a washing step (total n = 72), by liquid chromatography tandem mass spectrometry for Δ9-THC and CBD. Urines were tested for drug metabolites (LOD: 1.66 ng/ml). No accumulation of drugs over exposures was shown. Urines always tested negative. Washed hair samples were positive for CBD (mean 0.05 ng/mg) after exposure to low-Δ9-THC cannabis, and for Δ9-THC (mean 0.02 ng/mg) after exposure to high-Δ9-THC cannabis, with levels also typical of drug use. The two products could be easily distinguished. 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.