Dennis Jon McKenna (born December 17, 1950, in Paonia, Colorado)[1] is an American ethnopharmacologist, research pharmacognosist, lecturer and author.

[3] He received his doctorate in botanical sciences in 1984 from the University of British Columbia,[2] where he wrote a dissertation titled Monoamine oxidase inhibitors in Amazonian hallucinogenic plants: ethnobotanical, phytochemical, and pharmacological investigations.

McKenna then received post-doctoral research fellowships in the Laboratory of Clinical Pharmacology, National Institute of Mental Health, and in the Department of Neurology, Stanford University School of Medicine.

He co-authored The Invisible Landscape with his brother Terence and Botanical Medicines: the Desk Reference for Major Herbal Supplements with Kenneth Jones and Kerry Hughes.

[citation needed] His research has included the pharmacology, botany, and chemistry of ayahuasca and oo-koo-hé, the subjects of his master's thesis.