This study proposes to evaluate the effects of D-cycloserine (DCS) combined with Virtual Reality exposure therapy in a sample of patients who developed posttraumatic stress disorder (PTSD) following either the events of September 11, 2001, or military service in the war in Iraq. In addition, this study hopes to determine whether a common human genetic single nucleotide polymorphism (SNP) in a growth factor, brain derived neurotrophic factor, BDNF (Val66Met), predicts treatment response to PTSD.

Overall, this study aims 1) to determine if subjects administered DCS show a significantly larger decrease in symptoms of PTSD as compared to those administered a placebo, 2) to determine if subjects administered DCS show a decrease in PTSD symptomatology significantly earlier (as measured by weeks) than those administered a placebo, 3) to determine if differences in symptomatology are evident at a 6-month follow-up and indicate long-term differences between groups, and 4) to determine if the BDNF SNP predicts treatment response.

Participants with 9/11-related or military service in the Iraq War-related PTSD are assigned to one of two programs, following an initial assessment. Both programs include Virtual Reality Exposure Therapy (VRET) for the treatment of PTSD as well as widely-used standard cognitive-behavioral therapy techniques. The VRET is comprised of ten ninety minute sessions which involve mental imagery as well as virtual reality presentations delivered by a special display worn over the head and eyes. The virtual reality simulations consist of either images of the World Trade Center and the events of September 11, 2001 or multiple scenarios common to military personnel assigned to Iraq. One group of participants will receive the medication cycloserine (seromycin) and one group will receive a placebo drug (like a sugar pill). Participants take a dose of medication only on the days that they come to the laboratory for the Virtual Reality Exposure (VRE) sessions, and 90 minutes prior to the VRE sessions. Some subjects in the study will receive a 100 mg dose of cycloserine, and other subjects in the study will receive the placebo (sugar pill). This will be determined randomly (as by the flip of a coin). Neither the patient nor the treating clinicians will know which pill that patients are receiving; however, this arrangement may be changed if medically necessary. Patients are briefly assessed for well-being at every session, and are reassessed following session three, session six, and session ten for changes in symptomatology. At the completion of treatment and again six months later, the principal investigator or one of her associates will reinterview participants and have them complete some questionnaires.

Inclusion Criteria:

1. English-speaking adults
2. Between the ages of 18 and 70
3. Exposed to the WTC Attacks (were in towers or in the immediate area) or veterans of the Iraq War
4. Diagnosed with PTSD symptoms.

Exclusion Criteria:

1. Presence of current organic mental disorder
2. Schizophrenia
3. Bipolar disorder
4. Depression with psychotic features
5. Current substance dependence
6. Delusional disorder
7. Active suicidal ideation, intent, or plan
8. Active homicidal ideation, intent, or plan
9. Use of pacemaker
10. Medically unstable
11. Pregnant or lactating
12. A history of severe renal disease
13. History of seizures
14. Currently taking anticoagulants, ethionamide (Trecator-SC) or isoniazid (INH)
15. History of allergic reaction to cycloserine.