Drug has a pretty loose definition - anything with a physiological effect; but I was trained to think a drug as being those chemicals which can cross the blood brain barrier (BBB).

Alcohols can increase permeability of the BBB to solubilized substances in the blood so isopropyl would be able to affect the brain. Since a molecule has to cross lipid membranes (the capillary cell membranes etc) it’s most dependent on the polarity and size of the molecule.

any positive effects

This is another valid way to define a drug depending on which branch of science one is inclined to study but I prefer to think of this as merely adding a characteristic to that molecule; i.e. addictive qualities