Interference effects on verbal memory function, following oral lorazepam

Previous studies have consistently reported deficits in verbal memory following oral lorazepam administration. The possible role of susceptibility to interference effects as a contributory mechanism in benzodiazepine amnesia has not been examined as an independent variable. In addition, most studies of benzodiazepine amnesia have not controlled for the possible confounding effects of alcohol consumption, recently reported to affect the degree of amnesia produced by lorazepam. The present study assessed the verbal memory capabilities of 24 low social drinkers (MAST score < 3) receiving either oral lorazepam (2 mg) or placebo. Interference effects on verbal memory were assessed using the Auditory herbal Learning Test, with either the interference word list (trial B) or a counting backwards task. Lorazepam significantly reduced the recall scores for list B, compared to the first presentation of list A, suggesting lorazepam may increase susceptibility to proactive interference. There was no drug effect on retroactive interference. With regard to recall per se, lorazepam impaired verbal learning for initial acquisition trials (trials 2 and 3) but not subsequent trials, where learning was comparable to the placebo. Lorazepam did not produce significant impairment in immediate and delayed recall trials. This pattern of recall does not conform to the classic profile of benzodiazepine-induced amnesia; potential explanations for this are discussed.