For reasons unknown, only a little better than half the people treated with antidepressants respond to them… . studies have shown that placebos have only a slightly lesser rate of effectiveness than the drugs… . serotonin levels are affected by many things — exercise, light, sleep, diet and even time of day. And finally, serotonin has so much influence on chemistry and functions in so many places in the body and brain relating to mood, sleep, sexual desire, appetite and body temperature that to say that it acts in any one particular way is impossible.
