Psychoactive substances derived from plant materials have been used ritualistically for millennia (Schultes, Hofmann, & Rätsch, 2001). Simultaneous developments during the second half of the twentieth century in the biology of the mind and in synthetic organic chemistry have recast natural and synthetic intoxicants in a new biological and clinical light (Nichols, 2004). ese chemicals, referred to improperly as “hallucinogens,” alter psychoneurobiological behavior in ways both subtle and overt. e term hallucinogen implies an induction of hallucinations well known within clinical psychiatry, but this is not the case with most of the substances in question and some of them (i.e., entactogens such as MDMA) do not induce major sensory alterations. e terms psychotomimetics (psychosismimicking) or psychedelics have also been used. “Psychotomimetic” is not in common usage now, because, much as with “hallucinogen,” these substances are not primarily psychotogenic, whether mimicking or otherwise, although these drugs can exacerbate or contribute to worsening the mental health of those vulnerable to a formal thought disorder. “Psychedelic” may be the most commonly used lay term for hallucinogens and used to be an accepted alternate descriptor in the scientific literature. e psychiatrist Humphrey Osmond (1957) first offered this term meaning “mind manifesting” and called it “clear, euphonious and uncontaminated by other associations” (which apparently did weigh down the term by the end of the 1960s).