Dependencies do not only include physical things we take in, such as drugs or alcohol but might consist of essentially anything, such abstract things as gambling to relatively harmless items, such as chocolate - to puts it simply, addiction might describe a compound reliance (e.g. drug dependency) or behavioral dependency (e.g. betting addiction). pocket breathalyzer
This post focuses generally on dependency to physical substances.
In the past, dependency utilized to refer simply to psychoactive substances that cross the blood-brain barrier, temporarily modifying the chemical balance of the brain; this would consist of alcohol, tobacco, and some drugs.