drug (n.) Look up drug at Dictionary.com
late 14c. (early 14c. in Anglo-French), "medicine, chemical ingredients," from Old French droge "supply, stock, provision" (14c.), of unknown origin, perhaps from Middle Dutch or Middle Low German droge-vate "dry barrels," or droge waere, literally "dry wares," but specifically drugs and spices, with first element mistaken as word for the contents (see dry goods), or because medicines mostly consisted of dried herbs.

Compare Latin species, in Late Latin "wares," then specialized to "spices" (French épice, English spice). The same source produced Italian and Spanish droga, Swedish drog.

Application to "narcotics and opiates" is late 19c., though association with "poisons" is 1500s. Druggie first recorded 1968. To be a drug on or in the market (mid-17c.) is of doubtful connection and may be a different word, perhaps a play on drag, which was sometimes drug c.1240-1800.
drug (v.) Look up drug at Dictionary.com
c.1600, from drug (n.). Related: drugged; drugging.