Extension Study of Pimavanserin for the Adjunctive Treatment of Schizophrenia

Inclusion Criteria: 1. Patient is able to understand and provide signed informed consent 2. Has a caregiver or some other identified responsible person (e.g., family member, social worker, caseworker, or nurse) considered reliable by the Investigator in providing support to the subject to help ensure compliance with study treatment, study visits, and protocol procedures and who is also able to provide input helpful for completing study rating scale 3. Is completing the Week 6 visit in Study ACP-103-034 or the Week 26 visit in Study ACP-103-038 or 064 while continuing to take his/her assigned dose of blinded study drug and may, in the Investigator's opinion, benefit from continued adjunctive treatment with pimavanserin to a antipsychotic 4. If the subject is female, she must not be pregnant or breastfeeding. She must also be of non-childbearing potential (defined as either surgically sterilized or at least 1 year postmenopausal) or must agree to use two clinically acceptable methods of contraception 5. The main background antipsychotic with which the subject is being treated must continue to be on one of the antipsychotics listed below: * Aripiprazole * Aripiprazole long-acting injectables: * Abilify Maintena® * Aristada® * Asenapine * Risperidone * Risperidone long-acting injection * Olanzapine * Paliperidone extended release (ER) (≤9 mg) * Paliperidone palmitate * Invega Sustenna® (≤156 mg) * Invega Trinza® (≤546 mg) * Trevicta® (≤350 mg) * Xeplion® (≤100 mg) * Lurasidone * Cariprazine * Brexpiprazole * Asenapine Exclusion Criteria: 1. Patient is judged by the Investigator or the Medical Monitor to be inappropriate for the study (e.g., significantly noncompliant in Studies ACP-103-034, -038, or -064) 2. A urine drug screen (UDS) result at Baseline that indicates the presence of any tested prohibited substance of potential abuse 1. Subjects from Studies 034 and 038 with a result indicating the presence of marijuana are permitted, if allowed by medical regulations, if they agree to abstain from marijuana use during the study and the medical monitor approves the subject's participation 2. Subjects from Study 064 with a result indicating the presence of marijuana are not permitted in the study 3. Is taking a medication or drug or other substance that is prohibited according to this protocol 4. Known family or personal history or symptoms of long QT syndrome or risk factors for torsade de pointes and/or sudden death, including symptomatic bradycardia, hypokalemia or hypomagnesemia, and the presence of congenital prolongation of the QT interval 5. Patient has current evidence of a serious and/or unstable psychiatric, neurologic, cardiovascular, respiratory, gastrointestinal, renal, hepatic, hematologic, or other medical disorder, including cancer or malignancies, which would affect the patient's ability to participate in the study. 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).