Depression is a type of illness that affects a person's body, mood, and thoughts. It is not the same as a blue mood, and it cannot simply be willed away. In any given one-year period, almost 10 percent of the population suffers from depression. The condition often interferes with normal functioning and can cause pain and suffering, not only to those who have depression, but also to those who care about them. Possible symptoms of depression include feelings of hopelessness, irritability, and thoughts of death. Treatment options may involve medications, psychotherapy, or a combination of the two.