dope : (n.) 1807, American English, "sauce, gravy, thick liquid," from Dutch doop "thick dipping sauce," from doopen "to dip" (cf. dip (v.)). Extension to "drug" is 1889, from practice of smoking semi-liquid opium preparation. Meaning "foolish, stupid person" is older (1851) and may have a sense of "thick-headed." Sense of "inside information" (1901) may come from knowing before the race which horse had been drugged to influence performance. Dope-fiend is attested from 1896.
I am assuming that by bad dope you mean nothing more than bad drugs and from that standpoint I don't think there is a separate etymology for the pair.
It'd be the same as asking for the etymology of brick house.