Dimethyltryptamine (DMT) is a substituted tryptamine that occurs in many plants and animals, including human beings, and which is both a derivative and a structural analog of tryptamine. It is used as a psychedelic drug and prepared by various cultures for ritual purposes.
That was the textbook definition of DMT, and Terence McKenna has described his use of the substance as a way of giving himself a certain scientific clarity. Based on my personal experiences, not everyone needs mushrooms however to go on sucha trip: It has been found that the human brain produces DMT too, and this can for instance be the cause of delusions which are normally ascribed to psychological diseases.