antipsychotic drug vs major tranquilliser

antipsychotic drug and major tranquilliser both are nouns.

Word	Noun	Adjective	Verb	Adverb
antipsychotic drug	Yes	No	No	No
major tranquilliser	Yes	No	No	No

As nouns, antipsychotic drug and major tranquilliser are synonyms defined as:

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

antipsychotic drug (noun)	major tranquilliser (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