SSRI vs paroxetine

SSRI and paroxetine both are nouns.

Word	Noun	Adjective	Verb	Adverb
SSRI	Yes	No	No	No
paroxetine	Yes	No	No	No

As nouns, paroxetine is a hyponym of SSRI; that is, paroxetine is a word with a more specific, narrower meaning than SSRI:

SSRI: an antidepressant drug that acts by blocking the reuptake of serotonin so that more serotonin is available to act on receptors in the brain
paroxetine: a selective-serotonin reuptake inhibitor commonly prescribed as an antidepressant (trade name Paxil)

Other hyponyms of SSRI include fluoxetine, fluoxetine hydrocholoride, Prozac, Sarafem, Paxil, sertraline, Zoloft.

SSRI (noun)	paroxetine (noun)
an antidepressant drug that acts by blocking the reuptake of serotonin so that more serotonin is available to act on receptors in the brain	a selective-serotonin reuptake inhibitor commonly prescribed as an antidepressant (trade name Paxil)