Comparison of Δ9-tetrahydrocannabinol in venous and capillary blood following ad libitum cannabis smoking by occasional and daily users.

Δ9-Tetrahydrocannabinol (Δ9-THC) is the most prominent and main psychoactive cannabinoid found in cannabis. In forensic matters involving cannabis, such as drugged driving or workplace accident investigations, blood Δ9-THC determination is typically required. Venipuncture by a phlebotomist at a medical facility is often the standard blood collection protocol, but this procedure is time consuming and requires specialized training. Capillary blood collection at the site of a transportation or workplace mishap may provide a collection method that is logistically easier and may better reflect blood cannabinoid concentrations at the time of an incident. This study represents the first temporal comparison of the concentration of Δ9-THC and its primary metabolites in venous and capillary blood obtained from users following ad libitum inhalation of contemporary high-concentration cannabis products. Participants provided their own cannabis from a licensed Colorado dispensary and were instructed to smoke or vape ad libitum the amount most used for the desired effect during a 15-minute period. Capillary blood samples collected at the lateral shoulder using the TAP® II microneedle device and standard venipuncture samples at the forearm were collected contemporaneously at baseline and then 10, 30, 60, 90, and 140 minutes after the last inhalation and were analyzed for Δ9-THC, 11-hydroxy-Δ9-THC, and 11-carboxy-Δ9-THC by liquid chromatography tandem mass spectrometry. Within-subject Δ9-THC concentrations trended lower, often up to 30 to 40%, in contemporaneous capillary blood samples than in venous blood samples until 140 min after cannabis smoking. Concentrations of the Δ9-THC metabolites 11-hydroxy-Δ9-THC and 11-carboxy-Δ9-THC were equivalent at all but the first timepoint after smoking. Due to logistical advantages, capillary blood collection by microneedle devices may be a viable option for qualitative detection of Δ9-THC and its metabolites soon after an incident or a quantitative determination if the samples are collected at least 2 hours after cannabis inhalation.