Addiction doesn't result from emotional problems or character weakness, it causes them, write the authors. Addicts--whether to alcohol, drugs, nicotine or caffeine--have the same biochemical flaw, leading to a craving temporarily satisfied by some substance abuse. The flaw is inherited; if both parents are addicts, all their children are vulnerable. Depression often accompanies addiction and may be part of the same genetic defect. Janice Keller Phelps treats this theory as her own, but it's not new; there's some evidence in its favor.
Her discussion of therapy is also full of good sense. You stop an addiction by stopping--not by tapering, substituting or solving personal problems. Choosing to stop is fine, but it's OK to coerce someone. Since most addicts are depressed, that depression must be treated at the same time. A doctor's care is essential for most drug addiction, less useful for alcoholism and smoking. Addiction is lifelong; relapse is always possible.
There's an odd chapter on "sugar" addiction, plus repeated claims that massive vitamin therapy turns off craving and withdrawal symptoms "like magic." Editors often love this trendy fluff; the book might not have been acceptable without it. The author doesn't take it terribly seriously. Readers should do likewise, but it's probably harmless if they don't.