Increased susceptibility to memory intrusions and the Stroop interference effect during acute marijuana intoxication.

The marijuana-induced acute memory impairment was assessed in a double-blind, crossover experiment. Twelve males smoked NIDA-supplied cigarettes containing 1.2% delta-9-tetrahydrocannabinol (THC) or cannabinoid-exhausted marijuana (placebo) in counterbalanced order on 2 days 1-3 weeks apart. Practice, pre- and postsmoking test sessions were conducted with the Paced Auditory Serial Addition Test, Stroop Color and Word Test, and alternate forms of the Randt Memory Battery and the Controlled Oral Word Association Test. A significantly greater number of short story omissions and intrusions occurred in delayed free recall after marijuana. Immediate and sustained attention, controlled retrieval from semantic memory, and speed of reading and naming colors were not affected. The Stroop interference effect was significantly greater following marijuana. Subjects appeared to experience parallel difficulties in inhibiting associations to the new material and inhibiting the overlearned response of reading in a new learning task. Marijuana may compromise associative control, presumably a cognitive process inherent in memory function.