Justin E. H. Smith in Wired:
There is something strange in the disinterest philosophers show for experimentation with mind-altering drugs—or at least for talking about their experimentation publicly. At the margins of philosophical writing, we have Walter Benjamin’s record of his dabblings in hashish and Michel Foucault’s casual admission in interviews that he would rather be dropping acid in the Mojave Desert than sipping wine in Paris. Even further out we have philosophy-curious writers like Thomas de Quincey (also a biographer of Immanuel Kant) recounting his own experience of opium addiction. And then we have probabilities and speculation. The natural philosopher Johannes Kepler likely tried some fly agaric before writing his 1608 treatise of lunar astronomy, the Somnium (read it and you’ll see what I mean). The third-century Neoplatonist philosopher Plotinus might have availed himself of some herbal or fungal supplements to help him achieve his many out-of-body experiences, which he liked to call henosis, or “ecstatic union with the One.”
More here.