Freud liked the stuff so much that between roughly 1884 and 1896, when he was in his 20s and 30s and in his major cocaine period, he tended on many days to have a red, wet nose. He gave cocaine to family and friends. He employed it to “make bad days good and good days better,” the author writes, and to ease “the pain of being Sigmund.”

His letters to his fiancée were sometimes ripe with sexual feeling, of the kind a line of powder can incite. “I will kiss you quite red and feed you till you are plump,” Freud wrote. “And if you are forward you shall see who is the stronger, a gentle little girl who doesn’t eat enough or a big wild man who has cocaine in his body.”

Freud stopped using cocaine sometime around 1896, when he was 40, before writing the works that made him famous. Dr. Markel is careful not to link Freud’s drug use and his later ideas too intimately. But he offers shreds of tantalizing speculation.

Image A bottle of Vin Mariani, a 19th-century "tonic wine" that contained cocaine. Credit... Collections of the University of Michigan Center for the History of Medicine, Ann Arbor, Michigan

Recent scholarship, he writes, has offered “nuanced contemplations on the connection of Sigmund’s cocaine abuse to his signature ideas about accessing unconscious thoughts with talk therapy; the division of how our mind processes pleasure and reality; the interpretation of dreams; the nature of our thoughts and sexual development; the Oedipus complex; and the elaboration of the id, ego and superego.”