The effect of zolpidem and zopiclone on memory.

The effect of 10 mg of zolpidem (ZLP) on memory function was evaluated in healthy male adults using word recall test, passage recall test, and Sternberg's memory scanning task. This study was carried out as a double-blind cross-over study with 7.5 mg of zopiclone (ZPC) and a placebo. No difference was noted between the active drugs and placebo in the number of words recalled from the word list presented before administration. No evidence of retrograde amnesia was suggested. However, encoding ability was slightly affected as indicated by a decrease in the number of words recalled from the list presented after administration. Slight impairment of a delayed recall was noted for both of the active drugs, but the effect disappeared the next morning. In the memory scanning task, ZLP prolonged a non-specific component of reaction time 1.5 h after administration, but the effect disappeared after 12.5 h. ZPC did not prolong the reaction time. The two active drugs showed no specific effects on either memory scanning or response-selection stage in short-term memory at any time. The findings suggest that residual effects did not reach clinical significance at the standard dosage, although the active drugs slightly affected encoding ability and retention soon after administration.