There's nothing anachronistic about hashish in 19th-century France; it was a widely-known narcotic long before that. If you read Wikipedia's "history" entry, Du

There's nothing anachronistic about hashish in 19th-century France; it was a widely-known narcotic long before that. If you read Wikipedia's "history" entry, Dumas and Paris are explicitly name-checked (among a lengthy list of writers), - "In the 19th century, hashish was embraced in some European literary circles. Most famously, the Club des Hashischins was a Parisian club dedicated to the consumption of hashish and other drugs; its members included writers Théophile Gautier, Dr. Moreau de Tours, Victor Hugo, Alexandre Dumas, Charles Baudelaire and Honoré de Balzac.[19]" https://en.wikipedia.org/wiki/Hashish#History https://en.wikipedia.org/wiki/Hashish#History https://en.wikipedia.org/wiki/Club_des_Hashischins https://en.wikipedia.org/wiki/Club_des_Hashischins