Drug On The Market Meaning

(idiomatic) something which is overabundant at the moment and thus not in demand.

Example: for days and days he patrolled the town in vain; seeking for work, and finding none. The place, as his candid informer had said, was filled with clerks like himself in search of employment; and they, linguists especially, were a drug in the market — the cessation of the Franco-German War having flooded the country with foreign labour. — J.C. Hutcheson, "Fritz and Eric", 1880
...the bread fruit, roasted in the ashes of the fire, and the custard apples, with tea, furnished forth such a luxurious feast that all fears of possible starvation vanished, while the humble cocoanut at once became a drug on the market, useful enough perhaps as a thirst-quencher but otherwise of little value. — Harry Collingwood, "The Wreck of the Andromeda", 1923