Traditional psychedelics, such as LSD, psilocybin, or DMT, are psychoactive compounds that exert their effects mainly through agonism over serotonergic receptors. In appropriate doses and contexts, they produce profound changes in the subjective experience, configuring altered states of consciousness that, upon reaching a critical point, involve the appearance of phenomena of mystical, transcendental, or ego dissolution experiences. These events are associated with diverse therapeutic effects in several mental conditions. Psychedelics are safe substances, with minimal risk of serious or long-lasting adverse effects and without addictive potential. Current evidence comes from systematic reviews and meta-analyses based on phase II clinical studies, with small groups of subjects, strict exclusion criteria, and difficulties in applying the double-blind methodology. Worldwide there is a growing number of clinical trials, which seek to promote the approval of psychedelic-assisted therapies as therapeutic tools in the coming years. In this bibliographic review, we will address the phenomenological characteristics of the psychedelic experience, its potential therapeutic uses, and the mechanisms that underlie them.