The authors conducted a double-blind crossover study to investigate the effects of marijuana on visual information processing. The authors used a tachistoscopic paradigm, and the results show no marijuana effect on the critical stimulus duration, a measure of stimulus intake. The visual backward masking data are compatible with a marijuana-induced slowness of information processing from labile unconscious iconic memory to more permanent memory processes. These results are discussed in relation to reports of marijuana's effects on perception and early information processing.