How can one discern abuse from addiction?
"Discern" means to perceive, recognize or distinguish something. All experts in drug use, abuse and addiction state that it is difficult to discern (perceive, recognize, distinguish) abuse from addiction.
Addiction is clearly present when, in the absence of a supply of the drug of choice, a person has withdrawal symptoms associated with physical addiction of has emotional disorientation, like mood swings or worse, with psychological addiction.
Abuse is clearly present (though not necessarily) when legal or illegal drugs are taken in a way that breaches directions or common sense or that threatens, or even causes, harm to the individual.