The Placebo Effect is the amelioration of symptoms not attributable to medication—a kind of mental magic trick that has been shown to boost immunity and alleviate pain—even if you know it's all in your head.
Some 15 million Americans struggle with depression, an illness that comes in many forms—from major depression and seasonal affective disorder, to dysthymia and bipolar disorder. Depression is an illness that involves the body, mood, and thoughts.
It's amazing that a sugar pill can sometimes "fix" an ailment. Placebos are often prescribed, and sometimes to great therapeutic effect. Sometimes the simple act of believing you're going to get better can actually make you get better.