This historical review shows that the early history of cognitive psychopharmacology, originally labelled as "pharmacopsychology", is closely linked to developments in experimental psychology and academic psychiatry. At the beginning of his scientific career, the German psychiatrist Emil Kraepelin (1856-1926) joined Wilhelm Wundt's laboratory of experimental psychology at the University of Leipzig. Although Kraepelin was fired from his clinical position at the university's psychiatric hospital, he completed his habilitation, the German equivalent of Ph.D., and started a series of pharmacological investigations in healthy volunteers using common recreational drugs (alcohol, coffee, tea) or medicinal products (amyl nitrite, chloral hydrate, chloroform, ethyl ether, morphine, paraldehyde) together with innovative psychological tasks. This paper reviews Kraepelin's pharmacopsychological research and his methodological innovations, providing translations, for the first time, from original papers, his monograph On the Modulation of Simple Psychological Processes by Some Medicines and from other sources. Kraepelin's contributions to psychopharmacology and clinical neuropsychology were far ahead of his time and his conceptual achievements have been largely neglected by modern psychiatry and cognitive neuroscience.