Study of Preladenant for the Treatment of Neuroleptic Induced Akathisia (Study P05145)

Inclusion Criteria: * Participants or guardian must be willing to give written informed consent. * Part 1 Only: Participants with acute (not drug related) psychoses with a Positive and Negative Symptom Scale for Schizophrenia (PANSS) score of at least 60: schizophrenia, schizo-affective, schizo-manic, and acute mania with a history of previous treatment with neuroleptics. * Part 1 Only: Participants initiating haloperidol for the treatment of an acute psychotic episode at a dose of at least 7.5 mg per day. * Part 2 Only: Inpatient participants who have developed akathisia as a result of haloperidol at \>=5 mg per day for the treatment of acute psychosis. The enrollment of participants receiving other neuroleptics is allowed only after consultation and agreement by the sponsor. * Participants of either sex and of any race between the ages of 18 and 65 years, inclusive. * Participant's clinical laboratory tests (complete blood count \[CBC\], blood chemistry, and urinalysis) must be within normal limits or clinically acceptable to the investigator/sponsor. Participant's liver function test results (ie, aspartate aminotransferase \[AST\], alanine aminotransferase \[ALT\]) must not be elevated above the normal limits at Screening and on Day -1/1. * Participants must be free of any clinically significant disease other than psychosis that would interfere with the study evaluations. * Screening electrocardiogram (ECG) must be clinically acceptable to the investigator. * Female of childbearing potential must: * Have used a medically accepted method of contraception for 1 month (or abstained from sexual intercourse) prior to the screening period. An acceptable method of contraception includes one of the following: * condom (male or female) used with spermicide, * diaphragm or cervical cap used with spermicide and condom, * stable oral/transdermal/injectable hormonal contraceptive regimen without breakthrough uterine bleeding for 2 months prior to Screening visit and a condom used with spermicide, * intrauterine device (inserted at least 2 months prior to Screening visit) used with spermicide. Note: Vasectomy of the partner is not considered sufficient contraception and one of the 4 bulleted methods listed above must be used. * Agree to use one of the accepted methods of contraception (listed above) during the trial (including the screening period prior to receiving trial medication), and for 1 month after stopping the trial medication. * Participants enrolled in the placebo arm of Part 1 and who developed akathisia may be eligible for Part 2 in the standard of care arm. Exclusion Criteria: * Participants who have a positive screen for drugs with a high potential for abuse. Participants that screen positive for cannabis are permitted. * Participants who have previously received this compound. * Participants who are currently participating in another clinical study or have participated in a clinical study within 30 days (except participants enrolled in the Part 1 of the P05145 study). * Participants who are part of the study staff personnel or family members of the study staff personnel. * Participants with severe/uncontrolled hypertension will be excluded. Participants with hypertension well controlled on a stable dose of standard antihypertensive medication (excluding beta-blockers) will be eligible. * Participants with history of coronary artery disease including myocardial infarction (MI), or cerebrovascular disease (stroke, transient ischemic attack \[TIA\]), or peripheral arterial disease. * Participants with congestive heart failure or participants with ECGs consistent with ischemic heart disease, sick sinus syndrome or significant Q waves. * Participants who are found to be at immediate risk of suicide. * Female participants pregnant or nursing. * Participants treated by Clozapine will be excluded. A washout period of 6 months prior to dosing will be acceptable for study entry.