Twelve subjects received an oral dose of marihuana extract calibrated to 20 mg of δ
1-tetrahydrocannibinol on Day 1 of the experiment and performed a short-term memory task before and after administration of the drug. The subjects were then split into two groups, receiving either marihuana or placebo on the evenings of Days 1 to 4 and between two memory test sessions on Day 5. Placebo subjects showed little change in performance between the two test sessions on Day 5; however, results from Day 1 for all subjects and Day 5 for the drug group showed that reaction time increased from before- to after-challenge sessions. This increase in time under marihuana was explained as a change in encoding and/or response processes, rather than processes involved in the search of the memory store.