H+, e.g. (3)
(Other definitions for drug that I've seen before include "Maybe addictive substance" , "LSD, say" , "Perhaps grass" , "Substance used as medicine or narcotic" , "Substance used in medicine, often abused" .)
(Other definitions for ion that I've seen before include "Subatomic particle" , "Electrically charged particle" , "Charged atom/molecule" , "Eletrically charged particle" , "Electrically charged atom or group of atoms" .)