"empty, reduce, or exhaust by drawing away," 1807, originally in medicine (of blood-letting, purgatives), back-formation from depletion, which is from Latin deplere "to empty," literally "to un-fill," from de "off, away" (see de-) + plere "to fill" (from PIE root *pele- (1) "to fill"). General sense by 1859. Related: Depleted; depleting.
word-forming element making adjectives from verbs, meaning "pertaining to, tending to; doing, serving to do," in some cases from Old French -if, but usually directly from Latin adjectival suffix -ivus (source also of Italian and Spanish -ivo). In some words borrowed from French at an early date it has been reduced to -y (as in hasty, tardy).
<a href="https://www.etymonline.com/word/depletive">Etymology of depletive by etymonline</a>
Harper, D. (n.d.). Etymology of depletive. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/depletive