Whether Shankara and Plotinus and Meister Eckhart ever took psychedelics, who knows, but they may have just generated their own biochemical ingredients unconsciously.

This doctrine, according to Plotinus, is very ancient, and obscurely asserted even by Parmenides.

Exactly contemporary with him was the celebrated Ammonius the Porter, the teacher of Plotinus, and therefore the parent of Neo-Platonism.