Why don't anti-depressants work for most people?

The study led by Eva Redei, psychiatry professor at Northwestern University Feinberg School of Medicine (NUFSM), found powerful molecular evidence that quashes the popular dogma that stress generally triggers depression.
Her new research reveals that there is almost no overlap between stress-related genes and depression-related genes.
Her findings are based on extensive studies with a model of severely depressed rats that mirror many behavioural and physiological abnormalities found in patients with major depression.
"This is a huge study and statistically powerful," Redei said. "This research opens up new routes to develop new anti-depressants that may be more effective. There hasn't been an antidepressant based on a novel concept in 20 years."
She took four genetically different strains of rats and exposed them to chronic stress for two weeks. Later, she identified genes in the brain regions (linked with depression in rats and human), that had increased or decreased in response to the stress in all four strains.
"This finding is clear evidence that at least in an animal model, chronic stress does not cause the same molecular changes as depression does," said Redei, according to a NUFSM statement.
These findings were presented at a recent Neuroscience conference in Chicago.