OBJECTIVE

Cannabis has been shown to impair driving performance, but much of extant research has been conducted with relatively low concentration products, not reflective of the marketplace in states with legal adult recreational cannabis use. The study examined driving performance after cannabis use, inclusive of high concentration tetrahydrocannabinol (THC) products.

METHODS

Participants ( = 118) completed three 20-minute simulated drives, with rural and urban segments. The study was within-subjects; participants completed a pre-use (baseline) drive, and two post-use drives at approximately 30 min and an hour and a half after cannabis use. Of participants,  = 89 inhaled cannabis products (flower or concentrates) for up to 15 min and  = 29 participants completed the protocol without using cannabis. Outcomes included lane departures, standard deviation of lateral placement [SDLP], average speed, and standard deviation of speed. Primary predictors were time-point, and group based on cannabis use frequency and product used in the study (control group; occasional-flower; daily-flower; daily-concentrate).

RESULTS

There were significant changes in lane departures, SDLP and speed measures from baseline to post use, depending on the participant group and time point. When compared to the control group, the occasional-flower group had a greater increase in rate of lane departures (0.16 departures/minute at baseline and 0.47 at Post 1,  < 0.01). In contrast, the daily-concentrate group had an improvement in SDLP (27.2 to 26.1 cm at Post 1) compared to the control group (23.9 to 25.7 cm;  = 0.04). The daily-flower and occasional-flower groups had little to no change in average speed from pre- to post-cannabis use (e.g., 53.9 mph at baseline and Post 1, daily-flower group) whereas the control group increased speed (e.g., 53.9 to 54.6 mph, baseline to Post 1). There were additional significant differences between the groups. Within and between group differences in change were relatively small.

CONCLUSIONS

The occasional-flower group exhibited an increase in lane departures, not seen in other groups, consistent with tolerance in the daily-use groups. There was a notable absence of declines in driving performance for the daily-concentrate group. Changes in driving performance were relatively small across all groups.