Psychedelic plants and fungi have been used as medicinal and sacramental tools across cultural traditions since ancient times. The study of these drugs within modern clinical frameworks is relatively new, with an initial wave of research occurring in the mid-20 century and progressing until many of these substances became federally prohibited in the U.S. in the 1960s. Though further scientific investigation was limited for decades, a second wave of research began once more in the 1990s, thanks to work at Johns Hopkins University and other pioneering institutions. 

Psychedelics are known to produce thought, mood, and perceptual changes that are otherwise rarely experienced by people, and these effects are commonly viewed as insightful or personally meaningful. The subjective effects of these drugs have also been found to predictive of subsequent therapeutic benefit in clinical trials of psychedelics for various mental health conditions. "Classic" psychedelics are those that act primarily on serotonin-2A (5-HT2A) receptors in the brain. Other drugs like ketamine and MDMA produce overlapping effects but possess different mechanisms of action so are variably considered psychedelics. There are important similarities and differences between all of these drug types.

Ketamine and related compounds, like esketamine, are more often thought of as "dissociative" therapies, because of the characteristic experiences they produce, involving temporary feelings of detachment from one's usual sense of self or reality. Such effects have been shown to predict therapeutic benefit in some research studies and may be optimized when ketamine is administered with appropriate kinds of psychological support. This support is also thought to decrease the potential for negative outcomes that can occur with ketamine and psychedelic therapies. 

Please seek out expert medical and psychiatric advice before considering medications like ketamine or esketamine for the treatment of a mental health condition. Note that other psychedelic therapies, like psilocybin or MDMA, are not yet legal or approved for medical use in most settings.