Δ9-tetrahydrocannabinol (THC) can be measured in exhaled breath by using a simple aerosol particle collection device. The sampling procedure is simple, non-invasive and takes only 2–3 minutes. In the present study we measured the amount of THC in exhaled breath of cannabis users at specific time intervals up to three hours after smoking one cannabis cigarette. The breath concentration-effect relationship was studied by measuring the pulse rate and the pupil diameter to assess physiological changes.

Participants smoked self-supplied cannabis cigarettes, with an estimated content of 13 to 52mg of THC, corresponding to 248μg/kg to 693μg/kg. They smoked a cigarette outside for 5–10 minutes and directly after smoking, were called inside for breath sampling and physiological tests. Breath sampling was performed before smoking, directly after smoking and 15, 30, 60, 120, 180 minutes after smoking, with a SensAbues DrugTrap^® device (SensAbues AB, Huddinge, Sweden). The subjects were asked to breathe via a mouthpiece into a plastic bag for 2 to 3 minutes (± 20L of exhaled breath). THC was analyzed in exhaled breath by liquid chromatography-tandem mass spectrometry (Beck O et al. Journal of breath research. 2013;7(2):026006.). Thirteen subjects (9 males and 4 females, aged 23–24 years) have participated.

THC was detected in all breath samples but no THCCOOH (<LOD) was found in any sample. The mean THC concentrations were 1043, 27670, 14292, 10982, 4192, 3861 and 1479pg/filter before, immediately after and 15, 30, 60, 120 and 180 minutes after smoking. THC remained detectable for over three hours after smoking. Pulse rate (p=0.015) and pupil diameter (p=0.011) were significantly altered up to 30 minutes after smoking. The mean THC breath concentration showed a counter-clock wise hysteresis relationship with the mean pulse rate.

The detection window of cannabis in breath after smoking one cannabis cigarette in occasional and chronic smokers was at least 3 hours. Only tetrahydrocannabinol, not the metabolite, was detected. The tetrahydrocannabinol concentration in exhaled breath was related to the physiological changes that occur over time by a counterclockwise hysteresis loop. Exhaled breath can be used to detect recent cannabis exposure.