DEAR DOCTOR K: Is it true that some people are more vulnerable to addiction than others? Why?
DEAR READER: We tend to think about the ravages of addiction mainly when it takes a celebrity from us. Recently the actor Philip Seymour Hoffman died, at 46, of an apparent overdose of heroin. In 2012, it was the singer Whitney Houston, at 49. Both were once-in-a-generation talents -- and both gone, just like that.