A certain SSRI (can't mention the name as there was a suit involved) caused me permanent damage 10 years ago. I don't know a thing about genetics, but I suspect I'm one of those people who just shouldn't mess with their serotonin levels. I have strong reactions to the majority of meds that affect one's brain.
I did try Rozerem right after it came out. Believe it or not, it had no effect on me whatsoever. For sleep, Lunesta or Sonata work best, but my insurance will not cover them. So for me, it's zolpidem or nothing.
fanfaire