This study examined the duration of impairment of driving-related skills performance following marihuana use. Eight male subjects were examined in four experimental treatment test sessions at two-week intervals following training. A 20-minute performance battery consisted of three items:​ a visual search task involving the detection and recognition of signals presented randomly within a complex stimulus array, a divided-attention task requiring simultaneous performance of the visual search task and a compensatory tracking task and, finally, a critical tracking task. The test battery was administered 13 times over a 23-hour period on drug test days. A pre-dose test was followed by tests at 40-minute intervals for 4 hours, then at 2-hour intervals for 8 hours, with a final test battery at 23 hours.

Marihuana cigarette smoked at test sessions contained either 0, 50, 100 or 200 micrograms of delta-9 THC kg per B.W.

All three tasks exhibited drug-induced impairment with considerable variability in amplitude and duration of impairment among the tasks. The critical tracking task exhibited impairment for beyond 10 hours. Impairment magnitude of the high marihuana dose produced roughly double .07% alcohol impairment on the tracking task, whereas the alcohol impairment was greater on the visual search task than marihuana.

A replication of the study with eight additional subjects supported the conclusion that impairment duration of a single marihuana treatment extends well beyond the duration of the subjective "high."