English drogge appears late 14th century from Old French droge, supply or stock, origin unknown, per the OED's own confession. The leading derivation: Middle Dutch droge vate or droge waere, dry barrels, dry wares, the term for dried goods in trade, applied to drugs and spices because medicines were mostly dried herbs, the barrel's description mistaken for its contents. Compare dry goods, and Latin species, wares, narrowing to spices. The narcotics sense is only late 19th century; the poison association dates to the 1500s. The word has been a trade category wearing a white coat for six hundred years.
The phrase a drug on the market, a glutted, worthless commodity, is documented from 1661, and one trade history ties its currency to the 1833 deregulation of the Canton trade, when opium flooded Chinese ports and its price collapsed: the drug that was literally a drug on the market. Robinson Crusoe's cry at the wreck's coins, O Drug! what art thou good for, shows the word already meaning useless merchandise. The medicine and the cargo never separated, the apothecary and the smuggler selling the same dried wares to different customers.
The claim: drug is the archive's purest case of a word whose meaning is set by the state, not the substance, the same molecule a drug in the formulary, a drug in the indictment, and a drug on the market in the trade report, three legal statuses, one dried herb, the word functioning as a licensing stamp since the barrel. Verdict: the Harrison Act of 1914 and every scheduling schedule since are documented exercises in exactly this, attaching legality to the label. The Greeks had one honest word. The merchants had one honest barrel. Modern law has three dishonest categories, and the archive notes which of the three systems knew what it was selling.
If the word for the medicine is a merchant's mystery, what was in the barrel?