Abstract
Rationale
Memory plays a central role in the psychedelic experience. The spontaneous recall and immersive reliving of autobiographical memories has frequently been noted by researchers and clinicians as a salient phenomenon in the profile of subjective effects of classic psychedelic drugs such as psilocybin, LSD, and ayahuasca. The ability for psychedelics to provoke vivid memories has been considered important to their clinical efficacy.

Objective
This review aims to examine and aggregate the findings from experimental, observational, and qualitative studies on the acute modulation of memory by classic psychedelics in humans.

Method
A literature search was conducted using PubMed and PsycInfo as well as manual review of references from eligible studies. Publications reporting quantitative and/or qualitative findings were included; animal studies and case reports were excluded.

Results
Classic psychedelics produce dose-dependently increasing impairments in memory task performance, such that low doses produce no impairment and higher doses produce increasing levels of impairment. This pattern has been observed in tasks assessing spatial and verbal working memory, semantic memory, and non-autobiographical episodic memory. Such impairments may be less pronounced among experienced psychedelic users. Classic psychedelics also increase the vividness of autobiographical memories and frequently stimulate the recall and/or re-experiencing of autobiographical memories, often memories that are affectively intense (positively or negatively valenced) and that had been avoided and/or forgotten prior to the experience.

Conclusions
Classic psychedelics dose-dependently impair memory task performance but may enhance autobiographical memory. These findings are relevant to the understanding of psychological mechanisms of action of psychedelic-assisted psychotherapy.