Extension Study of Pimavanserin in Subjects With Major Depressive Disorder and Inadequate Response to Antidepressant Treatment

Inclusion Criteria: 1. Completed the antecedent study, Study ACP-103-054 or Study ACP-103-059 2. May benefit from longer term therapy with open-label pimavanserin treatment 3. If the subject is female, she must not be pregnant or breastfeeding. She must also be of nonchildbearing potential OR must agree to use acceptable methods of contraception Exclusion Criteria: 1. Is determined to be inappropriate for the study 2. Has developed neurologic, cardiovascular, respiratory, gastrointestinal, renal, hepatic, hematologic, or other medical or mental disorder, including cancer or malignancies that would affect the patient's ability to participate in the program Additional inclusion/exclusion criteria apply. Patients will be evaluated at screening to ensure that all criteria for study participation are met. Patients may be excluded from the study based on these assessments (and specifically, if it is determined that their baseline health and psychiatric condition do not meet all pre-specified entry criteria).