drug addiction vs dependency

drug addiction and dependency both are nouns.

Word	Noun	Adjective	Verb	Adverb
drug addiction	Yes	No	No	No
dependency	Yes	No	No	No

As nouns, dependency is a hypernym of drug addiction; that is, dependency is a word with a broader meaning than drug addiction:

drug addiction: an addiction to a drug (especially a narcotic drug)
dependency: being abnormally tolerant to and dependent on something that is psychologically or physically habit-forming (especially alcohol or narcotic drugs)

Other hypernyms of drug addiction include addiction, dependance, dependence, habituation.

drug addiction (noun)	dependency (noun)
an addiction to a drug (especially a narcotic drug)	a geographical area politically controlled by a distant country
	the state of relying on or being controlled by someone or something else
	being abnormally tolerant to and dependent on something that is psychologically or physically habit-forming (especially alcohol or narcotic drugs)