Dennis McKenna is an ethnopharmacologist with a special interest in naturally occurring psychedelic substances.  He was a cofounder of the psychedelic research non-profit the Heffter Research Institute where he is director of ethnopharmacology.  With his brother Terrence he authored the classic books The Invisible Landscape and the Magic Mushroom Grower's Guide and more recently he has written books including a memoir titled The Brotherhood of the Screaming Abyss.  Our conversation focuses on the place of psychoactive substances such as psilocybin and dimethyltryptamine (DMT) in nature and the effects they have on humans. You can find out about his current work at the McKenna Academy for Natural Philosophy at www.mckenna.academy