A reader asks if there is any difference between addiction and dependency.
The Chicago Manual of Style offers this straightforward distinction:
One is physically addicted to something but psychologically dependent on something.
I like the simplicity of this explanation, but a casual Web tour reveals a difference of opinion when the context is drug use. For example:
Physical dependence in and of itself does not constitute addiction, but it often accompanies addiction.—National Institute on Drug Abuse (US government site).
A number of substances produce psychological and/or physical dependence without producing an addiction.—Addiction Science Forum.
Addiction can occur without physical dependence [and] physical dependence can occur without addiction.—The National Alliance of Advocates for Buprenorphine Treatment.
Clearly, the use of the words dependency and addiction must be handled with care when writing about their medical implications. For the non-medical writer whose purpose is to choose between the words on the basis of connotation, a look at their etymologies offers a basis for choice.
Addiction implies enslavement. The word derives from a Latin verb that meant, among other things, “to sell into slavery.” An addicted person no longer belongs to himself. Addiction implies a state from which there is no escape.
Dependency, on the other hand, carries the connotation of temporality. A child’s dependency ends with maturity. Dependency connotes a situation from which there is a way out.