When your hero is on a quest to murder his father and maybe burn his house down along the way, drugs are a sensible thing to leave out of the equation. Most mushrooms in Symphony of the Night, for instance, are of the harmless edible variety, and the rest are deadly poisonous. This is Konami, teaching you valuable lessons about not eating dangerous things. Educational!
However, Alucard's rather more trusting with man-made substances. He'll eat a tab of paper that transports him across space and time; given the chance, he'll toy with the even more LSD-esque Holy Glasses, which grant visions of strange glowing orbs and allow users to experience the world afresh.
Everything in the LSD world of the Upside-Down Castle is topsy-turvy and crazy-colored, as our hero experiences visions of forgotten spiritual trauma and familial unease. The founder of Alcoholics Anonymous, dosed with LSD during his own substance-abuse therapy, reported similar experiences; nowadays, doctors prefer the less salacious but somewhat safer method of “talking about things.” Luckily for players, Alucard apparently doesn't believe in therapy.