Amnesia

Amnesia is the failure to form or retain memories of events that occur while a substance is active.

As a drug effect it is acute and high-dose-dependent, resolving as the substance wears off, which distinguishes it from clinical amnestic syndromes. It ranges from patchy recall of isolated moments to a complete blackout — a state in which a person may appear fully conscious and functional while encoding nothing at all.

It is uncommonly reported across psychoactive substances. It is most commonly induced at high doses under dissociatives such as ketamine, dextromethorphan, and 3-MeO-PCP, and under depressants such as diazepam and 1,4-butanediol; it also appears at high doses under deliriants such as datura and Amanita muscaria, and occasionally under psychedelics such as LSD, 25B-NBOH, and 25C-NBOH.

Amnesia is felt as discontinuity: moments arrive without context, and stretches of time are simply absent from memory. People may surface mid-scene — a room changed, a different face nearby — with no thread connecting what came before.

It commonly comes with present-tense confusion, an inability to track elapsed time, and a sense of having missed something without knowing what. Trying to recover the missing period deepens the disorientation. At high doses, particularly under dissociatives, the gaps can be total — a person acts and speaks while encoding nothing.

Amnesia arises through different pathways depending on the drug class:

• Dissociatives — block NMDA receptors, disrupting the glutamatergic signaling required to consolidate new memories; encoding fails while behavior continues.
• Depressants — potentiate GABA-A receptors; at high doses this suppresses hippocampal activity sufficiently to prevent the formation of new memories.
• Deliriants — block muscarinic acetylcholine receptors; acetylcholine is essential to memory encoding, and its blockade produces dense anterograde amnesia.
• Psychedelics — the mechanism is less clear; amnesia is rare and may reflect dose-dependent disruption of hippocampal function at very high doses.

How much each pathway contributes in a given case is not fully understood.

Who experiences it, and how strongly, varies widely. Dose is the dominant factor — amnesia is largely a high-dose phenomenon and rarely appears at low or moderate doses. Combining depressants with dissociatives or alcohol substantially lowers that threshold.

Individual differences in drug metabolism, body weight, and whether the substance was taken on an empty stomach all shift susceptibility. Prior experience with a substance offers little protection; unlike set-and-setting effects, amnesia cannot be managed through mindset alone, which makes it harder to detect or prevent while it is occurring.