1
general::
A commodity whose supply greatly exceeds the demand for it. For example, Now that asbestos is considered dangerous, asbestos tile is a drug on the market. The use of the noun drug in the sense of "something overabundant" (as opposed to a medicine or narcotic) dates from the mid-1600s, but the first record of the full expression, put as drug in the market, dates only from the 1830s.
American Heritage Idioms
2
general::
Phrase(s): a drug on the market [and] a glut on the market
something that is on the market in great abundance. • Right now, small computers are a drug on the market. • Twenty years ago, small transistor radios were a glut on the market.
McGrawhill's American Idioms And Phrasal Verbs