This is a 12-week, double-blind, placebo-controlled study on the efficacy, tolerability and safety of oral ziprasidone as monotherapy in patients with (major depressive disorder) MDD. The study involves the enrollment of a total of 120 patients with MDD over the course of 12 months across two sites. Outpatients suffering from MDD will be treated with either ziprasidone or with placebo for 12 weeks using the sequential parallel comparison design.

In light of the challenge major depressive disorder (MDD) poses to clinicians and patients alike, identifying novel treatments is urgently needed to help further refine the standard of care. Judging by their molecular structure and function, the atypical neuroleptic agents offer possibilities as effective antidepressants. To date, several studies have been reported examining the use of atypical neuroleptic agents as adjunctive therapy (used along with an antidepressant) for MDD. These studies go so far as to suggest that atypical neuroleptic agents have potential for treating MDD. Until now, atypical neuroleptics have been strictly viewed as adjuncts, however, it is quite possible that some of the atypical neuroleptic agents may possess antidepressant properties when used as the lone therapy.

The atypical neuroleptic agent ziprasidone, in particular, is an excellent neuroleptic candidate for studying antipsychotic effects on MDD for two principal reasons: its structure makes it favorable for binding to neurotransmitters in the brain and it has fewer side-effects compared to the other drugs in its class. This study will be the first, double blind, placebo-controlled trial of ziprasidone as monotherapy for MDD. If safe and effective as an antidepressant, ziprasidone would represent an additional option for patients with MDD.

Potential subjects will be approached during a regularly scheduled clinic visit, upon referral from another physician, or in response to research advertisements. Interested individuals will have the opportunity to review the consent form with family, friends, and other physicians prior to making a final decision regarding study enrollment. Once the subject has given informed consent, the screening process for the study will commence.

Subjects will have a screening visit to determine eligibility. The screening visit consists of a medical evaluation, completion of psychological rating scales, physical/neurological exams, electrocardiogram, and the collection of blood and urine. After subjects pass screening, they will be randomized into one of 3 study groups. Subjects will receive either 12 weeks of ziprasidone, 12 weeks of placebo, or 6 weeks of placebo followed by 6 weeks of ziprasidone. Study participants will have a 5 in 8 chance of receiving ziprasidone at some point in the study.

Subjects will be closely monitored during the study via 2 phone calls weekly from the study coordinator. The overall safety of the study will also be well scrutinized. The investigators shall identify an independent physician safety monitor, who will be without any affiliation to this study. He/she will be provided all the information necessary to evaluate the study's safety parameters and whether or not they are effective preventative measures.

Various psychological assessments will be completed by research subjects at every study visit.

This research study is designed to test the safety and/or effectiveness of the investigational use of the drug Ziprasidone that has been approved by the U.S Food and Drug Administration (FDA). While the drug used in the study is FDA-approved for treating schizophrenia and Bipolar disorder I, it is not yet approved for alleviating solely the symptoms of depression.