Depression is a serious illness that affects a person's body, mood, and thoughts. Known medically as major depression, major depressive disorder, clinical depression, and unipolar disorder, symptoms can include restlessness and irritability; feelings of guilt, worthlessness, and helplessness; and persistent physical symptoms that do not respond to treatment. Risk factors for depression include a history of substance abuse, certain medical illnesses (such as a stroke), and a family history of the condition. Depression is often treated with medications, psychotherapy, or a combination of the two.