Freud on Drugs

Remember that marvelous passage in Civilization and Its Discontents where Freud—anticipating what research into cognition has already confirmed—suggests that the psychic effects of drugs are identical with those that can be induced by other stimuli?

'[I]t is a fact that there are foreign substances which, when present in the blood or tissues, directly cause us pleasurable sensations; and they also so alter the conditions governing our sensibility that we become incapable of recovering unpleasurable impulses.... But there must be substances in the chemistry of our own bodies which have similar effects.'

Singular.