alpha-blocker vs blocking agent

alpha-blocker and blocking agent both are nouns.

Word	Noun	Adjective	Verb	Adverb
alpha-blocker	Yes	No	No	No
blocking agent	Yes	No	No	No

As nouns, blocking agent is a hypernym of alpha-blocker; that is, blocking agent is a word with a broader meaning than alpha-blocker:

alpha-blocker: any of various drugs that block alpha-adrenergic receptors; used in treating benign prostatic hyperplasia; relaxes the muscles of the prostate and bladder
blocking agent: a class of drugs that inhibit (block) some biological process

Other hypernyms of alpha-blocker include blocker.

alpha-blocker (noun)	blocking agent (noun)
any of various drugs that block alpha-adrenergic receptors; used in treating benign prostatic hyperplasia; relaxes the muscles of the prostate and bladder	a class of drugs that inhibit (block) some biological process