It usually takes three to six weeks for antidepressants to work in humans—perhaps coincidentally, the same amount of time it takes for newly born neurons in the hippocampus to mature, extend their projections, and connect with other neurons. So we may, without knowing it, have been helping people get out of depression by using medications that foster brain plasticity. Since people who improve in psychotherapy also find that their memories improve, it may be that it also stimulates neuronal growth in their hippocampi.
