Please answer! what makes people develop manic depression?

Bipolar Disorder: "manic depression" is an older term for bipolar disorder, which involves mood instability with periods of depression and mania. There is usually some family disposition, with exacerbating environmental influences such as drug and alcohol abuse, sleep disturbance, certain medications like steroids, etc. Sometimes the correct diagnosis isn't discovered until an antidepressant induces mania.

MANIC DEPRESSION: It is advisable to have an evaluation by a Psychiatrist to determine the factors involved in your problem. Each person is unique and generalizations may not apply to you. This is an illness that needs both correct medication and psychotherapy with a Clinical Psychologist.