antipsychotic agent vs major tranquillizer

antipsychotic agent and major tranquillizer both are nouns.

Word	Noun	Adjective	Verb	Adverb
antipsychotic agent	Yes	No	No	No
major tranquillizer	Yes	No	No	No

As nouns, antipsychotic agent and major tranquillizer are synonyms defined as:

antipsychotic agent and major tranquillizer: tranquilizer used to treat psychotic conditions when a calming effect is desired

antipsychotic agent (noun)	major tranquillizer (noun)
tranquilizer used to treat psychotic conditions when a calming effect is desired	tranquilizer used to treat psychotic conditions when a calming effect is desired