I didn't know what serotonin was until I found out I didn't have enough of it. I hadn't been sleeping well--for years, it seemed--and I went to my general practitioner for help. I described a pattern of waking up two or three times every night. "That's textbook," my doctor said. "Textbook what?" I asked. He stunned me by answering, "Textbook depression."

Though I was pretty sure I didn't need it, I went home with a prescription for amitriptiline, a tricyclic antidepressant of the pre-Prozac age. The crinkly pamphlet that came with the pills mentioned some side effects: weight gain, dry mouth,...

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