What was Jekyll’s drug of dependence? While alcohol is and was the most common drug of abuse, and Stevenson himself was known to have used alcohol, for a number of reasons we think it was not Jekyll’s drug of choice. First, Jekyll twice mentions alcohol by way of comparison to his potion (pp. 82, 92), with the implication that his potion is not merely ethanol. As well, the cardinal symptom associated with taking the potion—the vivid perception that Hyde is smaller than Jekyll—does not seem consistent with alcohol dependence. Other drugs that Stevenson was known to have used are hashish and opium (4, 5), but use of neither of these drugs would be consistent with Hyde appearing to be smaller than Jekyll. As well, the often marked activity of Hyde, including the murder of Sir Danvers Carew, would not be consistent with opium dependence.