pain pill vs medicinal drug

pain pill and medicinal drug both are nouns.

Word	Noun	Adjective	Verb	Adverb
pain pill	Yes	No	No	No
medicinal drug	Yes	No	No	No

As nouns, medicinal drug is a hypernym of pain pill; that is, medicinal drug is a word with a broader meaning than pain pill:

pain pill: a medicine used to relieve pain
medicinal drug: (medicine) something that treats or prevents or alleviates the symptoms of disease

Other hypernyms of pain pill include medicament, medication, medicine.

pain pill (noun)	medicinal drug (noun)
a medicine used to relieve pain	(medicine) something that treats or prevents or alleviates the symptoms of disease