He spoke and wrote about a variety of subjects, including psychedelic drugs, plant-based entheogens, shamanism, metaphysics, alchemy, language, philosophy, culture, technology, ethnomycology, environmentalism, and the theoretical origins of human consciousness.

[3][13] McKenna said that one of his early psychedelic experiences with morning glory seeds showed him "that there was something there worth pursuing",[13] and in interviews he claimed to have smoked cannabis daily since his teens.

[6][22][23] After his mother's death[24] from cancer in 1970,[25] McKenna, his brother Dennis, and three friends traveled to the Colombian Amazon in search of oo-koo-hé, a plant preparation containing dimethyltryptamine (DMT).

They hypothesised this would give them access to the collective memory of the human species, and would manifest the alchemists' Philosopher's Stone which they viewed as a "hyperdimensional union of spirit and matter".

[16] The voice's reputed revelations and his brother's simultaneous peculiar psychedelic experience prompted him to explore the structure of an early form of the I Ching, which led to his "Novelty Theory".

The new technique involved the use of ordinary kitchen implements, and for the first time the layperson was able to produce a potent entheogen in his [or her] own home, without access to sophisticated technology, equipment, or chemical supplies.

[39] In addition to psychedelic drugs, McKenna spoke on a wide array of subjects,[26] including shamanism; metaphysics; alchemy; language; culture; self-empowerment; environmentalism, techno-paganism; artificial intelligence; evolution; extraterrestrials; science and scientism; the Web; and virtual reality.

We must decondition ourselves from 10,000 years of bad behavior, and it's not easy.McKenna soon became a fixture of popular counterculture[5][6][37] with Timothy Leary once introducing him as "one of the five or six most important people on the planet"[41] and with comedian Bill Hicks' referencing him in his stand-up act[42] and building an entire routine around his ideas.

[49] The 19-acre (7.7 ha) botanical garden[3] is a repository containing thousands of plants that have been used by indigenous people of the tropical regions, and includes a database of information related to their purported healing properties.

According to Wired magazine, McKenna was worried that his tumor may have been caused by his psychedelic drug use, or his 35 years of daily cannabis smoking; however, his doctors assured him there was no causal relation.

There is no set rule to avoid being overwhelmed, but move carefully, reflect a great deal, and always try to map experiences back onto the history of the race and the philosophical and religious accomplishments of the species.

"[56]He also recommended, and often spoke of taking, what he called "heroic doses",[32] which he defined as five grams of dried psilocybin mushrooms,[6][57] taken alone, on an empty stomach, in silent darkness, and with eyes closed.

He proposed that DMT sent one to a "parallel dimension"[8] and that psychedelics literally enabled an individual to encounter "higher dimensional entities",[58] or what could be ancestors, or spirits of the Earth,[59] saying that if you can trust your own perceptions it appears that you are entering an "ecology of souls".

[76][77] McKenna stated that, due to the desertification of the African continent at that time, human forerunners were forced from the shrinking tropical canopy into search of new food sources.

[6] He believed they would have been following large herds of wild cattle whose dung harbored the insects that, he proposed, were undoubtedly part of their new diet, and would have spotted and started eating Psilocybe cubensis, a dung-loving mushroom often found growing out of cowpats.

[79] At these higher doses, McKenna also argued that psilocybin would be triggering activity in the "language-forming region of the brain", manifesting as music and visions,[3] thus catalyzing the emergence of language in early hominids by expanding "their arboreally evolved repertoire of troop signals".

[7][8][27][78] McKenna's "stoned ape" theory has not received attention from the scientific community and has been criticized for a relative lack of citation to any of the paleoanthropological evidence informing our understanding of human origins.

Criticism has also noted a separate study on psilocybin-induced transformation of visual space, wherein Fischer et al. stated that psilocybin "may not be conducive to the survival of the organism".

[81] Others have pointed to civilizations such as the Aztecs, who used psychedelic mushrooms (at least among the Priestly class), that did not reflect McKenna's model of how psychedelic-using cultures would behave, for example, by carrying out human sacrifice.

McKenna pointed to phenomena including surrealism, abstract expressionism, body piercing and tattooing, psychedelic drug use, sexual permissiveness, jazz, experimental dance, rave culture, rock and roll and catastrophe theory, amongst others, as his evidence that this process was underway.

[8] The basis of the theory was conceived in the mid-1970s after McKenna's experiences with psilocybin mushrooms at La Chorrera in the Amazon led him to closely study the King Wen sequence of the I Ching.

[88] Population growth, peak oil, and pollution statistics were some of the factors that pointed him to an early twenty-first century end date and when looking for a particularly novel event in human history as a signal that the final phase had begun McKenna picked the dropping of the atomic bomb on Hiroshima.

[5][94][b] McKenna saw the universe, in relation to novelty theory, as having a teleological attractor at the end of time,[5] which increases interconnectedness and would eventually reach a singularity of infinite complexity.

Some projected dates have been criticized for having seemingly arbitrary labels, such as the "height of the age of mammals"[11] and McKenna's analysis of historical events has been criticised for having a eurocentric and cultural bias.

In a 1993 letter to The New York Times, he wrote that: "surely the fact that Terence McKenna says that the psilocybin mushroom 'is the megaphone used by an alien, intergalactic Other to communicate with mankind' is enough for us to wonder if taking LSD has done something to his mental faculties.

"[17] The same year, in his True Hallucinations review for The New York Times, Peter Conrad wrote: "I suffered hallucinatory agonies of my own while reading his shrilly ecstatic prose".

[17] Reviewing Food of the Gods, Richard Evans Schultes wrote in American Scientist that the book was "a masterpiece of research and writing" and that it "should be read by every specialist working in the multifarious fields involved with the use of psychoactive drugs".

"[97] In 1994, Tom Hodgkinson wrote for The New Statesman and Society, that "to write him off as a crazy hippie is a rather lazy approach to a man not only full of fascinating ideas but also blessed with a sense of humor and self-parody".

[17] In a 1992 issue of Esquire magazine, Mark Jacobson wrote of True Hallucinations that, "it would be hard to find a drug narrative more compellingly perched on a baroquely romantic limb than this passionate Tom-and-Huck-ride-great-mother-river-saga of brotherly bonding," adding "put simply, Terence is a hoot!

"[6] Wired called him a "charismatic talking head" who was "brainy, eloquent, and hilarious",[27] and Jerry Garcia of the Grateful Dead also said that he was "the only person who has made a serious effort to objectify the psychedelic experience".