Amnesia can be described as an inability to later recall the events which occurred under the influence of a substance after it has worn off. During states of amnesia, a person will usually retain a functional short-term memory which can still recall events that recently occurred despite those same events failing to later form into long-term memories. As such, a person experiencing amnesia may not obviously appear to be doing so, as they can often carry on normal conversations and perform complex tasks.
This state of mind is commonly referred to as a "blackout", an experience that can be divided into 2 formal categories, "fragmentary" blackouts and "en bloc" blackouts. Fragmentary blackouts, sometimes known as "brownouts", are characterized by having the ability to recall specific events from an intoxicated period but remaining unaware that certain memories are missing until reminded of the existence of those 'gaps' in memory. Studies suggest that fragmentary blackouts are far more common than "en bloc" blackouts. In comparison, En bloc blackouts are characterized by a complete inability to later recall any memories from an intoxicated period, even when prompted. It is usually difficult to determine the point at which this type of blackout has ended as sleep typically occurs before this happens.
Amnesia is often accompanied by other coinciding effects such as disinhibition, sedation, and memory suppression. It is most commonly induced under the influence of heavy dosages of GABAergic depressant compounds, such as alcohol, benzodiazepines, GHB, and zolpidem. However, it can also occur to a much lesser extent under the influence of very heavy dosages of hallucinogenic compounds such as psychedelics, dissociatives, Salvia divinorum, and deliriants.
Compounds within our psychoactive substance index which may cause this effect include:
- Responsible use
- Subjective effects index
- Memory enhancement
- Dissociatives - Subjective effects
- Deliriants - Subjective effects
- Psychedelics - Subjective effects
- Fragmentary and en bloc blackouts: similarity and distinction among episodes of alcohol-induced memory loss | https://www.ncbi.nlm.nih.gov/pubmed/12921196
- Experiential aspects of alcohol-induced blackouts among college students. | https://www.ncbi.nlm.nih.gov/pubmed/15083562
- Alcoholic "blackouts": a review and clinical study of 100 alcoholics | https://www.ncbi.nlm.nih.gov/pubmed/5804804