Monoamine oxidase
McKenna received his Master's degree in botany at the University of Hawaii in 1979. He received his doctorate in botanical sciences in 1984 from the University of British Columbia, where he wrote a dissertation entitled "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.