Lurasidone HCI is a compound that is a candidate for the treatment of bipolar I depression. This clinical study is designed to test the hypothesis that Lurasidone in combination with either Lithium or Divalproex is effective among patients with bipolar I depression.

Inclusion Criteria:

1. Provide written informed consent and is 18 to 75 years of age inclusive.
2. Meets DSM-IV-TR criteria for bipolar I disorder, most recent episode depressed (≥ 4 weeks and less than 12 months) without psychotic features.
3. Has a lifetime history of at least one bipolar manic or mixed manic episode.
4. Currently being treated with lithium or divalproex or willing to begin treatment with lithium or divalproex.
5. Not pregnant or nursing and is not planning pregnancy within the projected duration of the study.
6. Females of reproductive potential agree to remain abstinent or use adequate and reliable contraception throughout the study and for at least 30 days after
7. Good physical health on the basis of medical history, physical examination, and laboratory screening.

Exclusion Criteria:

1. Subject is considered by the investigator to be at imminent risk of suicide or injury to self, others, or property.
2. Any chronic organic disease of the CNS (other than Bipolar I Disorder).
3. Hospitalization for a manic or mixed episode within the past two months.
4. Used investigational compound within past 6 months.
5. Clinically significant history of alcohol or substance abuse within the past 3 months or alcohol or substance dependence within the past 12 months.