Anterograde and Retrograde Amnesia after Lormetazepam and Flunitrazepam

Abstract

In a pharmacopsychological study, memory impairments after single oral doses of benzodiazepines or placebo were investigated in 40 healthy men aged 20–40 years. The study was designed as a double-blind and placebo-controlled trial. Four independent groups of 10 subjects randomly received either 1 mg lormetazepam, 2 mg lormetazepam, 2 mg flunitrazepam, or placebo. The tests consisted of word lists, picture tests, and syllable pairs (consonant-vowel-consonant tri-grams). Tests were performed before drug ingestion, and 1, 2, 3, and 5 h after application. Different test versions were used on each occasion. The target variables were immediate recall (after presentation and a 10-s distraction task) and delayed recall and recognition (after 30 min). Recognition was also tested after 24 h for all five versions.

A distinction must be made between anterograde amnesic effects and retrograde amnesic effects. The greatest anterograde memory impairments were observed after 2 mg flunitrazepam (p < 0.05). Lormetazepam 2 mg produced less marked impairments than flunitrazepam. Results after 1 mg lormetazepam did not differ from those after placebo. Performance in the memory tests was better under benzodiazepines than under placebo as regards material learned before drug ingestion, i.e. the benzodiazepines had not negative retrograde amnestic effects, but rather “promnesic” effects.

The results suggest that the extent of the benzodiazepines’ amnesic effects — both negative (anterograde) and positive (retrograde) — depends on the dosage and type of substance.