Addiction refers to a physiological and/or psychological condition that determines behavior based upon driving needs. Abuse refers to actions taken regardless of known adverse consequences. Thus, in the simplest analysis, addiction versus abuse may be described as compulsive drive versus choice of action.
In addiction, the substance resulting in physio-psychological addiction causes a rearrangement of physiological and/or psychological chemical balances, impulses, motivational drives so that behavior that was formerly based upon rational choice (good or bad rational choice) becomes compulsive thus beyond the regulation of rational thought and selection mechanisms.
In abuse, the individual may know of or even experience adverse consequences from taking or over-taking substances yet chooses (without physical or psychological compulsion mechanisms overriding rational processes) to continue to take the substance for one reason or another.
The very essence of addiction is different from abuse. Addiction occurs when substance characteristics override human volition (choice) and render actions compulsive. Abuse occurs when harmful choices are made through the agency of human volition but that lead to known harm.