Among the most important of Freud's accomplishments were his transition from physiology to psychology, the discovery of the unconscious, his demonstration of the significance of sexuality in the etiology of the neuroses, the therapeutic utilization of free association, the scientifically grounded interpretation of dreams, and his self-analysis. Ordinarily, his stay with Charcot in Paris (1885-1886) is regarded as the beginning of this creative period, and the end of his friendship with Fliess is taken to be its termination. The author submits the thesis that the drug, cocaine, which Freud made temporary use of in the 1880's, played a greater role in the creation of psychoanalysis than has been assumed to date. Above all, in The Interpretation of Dreams there are a great many references to alkaloids. These may be considered a result (and resolution) of a protracted unconscious effort to come to grips with cocaine euphoria.