dosage vs medication

dosage and medication both are nouns.

Word	Noun	Adjective	Verb	Adverb
dosage	Yes	No	No	No
medication	Yes	No	No	No

As nouns, medication is a hypernym of dosage; that is, medication is a word with a broader meaning than dosage:

dosage: a measured portion of medicine taken at any one time
medication: (medicine) something that treats or prevents or alleviates the symptoms of disease

Other hypernyms of dosage include medicament, medicinal drug, medicine.

dosage (noun)	medication (noun)
a measured portion of medicine taken at any one time	the act of treating with medicines or remedies
the quantity of an active agent (substance or radiation) taken in or absorbed at any one time	(medicine) something that treats or prevents or alleviates the symptoms of disease