I take an antideppresant.It took 4 weeks for me to feel any positive effects ,in fact for the first four weeks I felt worse due to the side effects which are crappy for most people for the first few weeks you feel more depressed.
They are not a placeibo effect. If I wake up feeling depressed, 45 mins after taking one tablet I can no longer lie in bed and want to get things done. They play with seratonin levels a bit like e's