This study is designed to investigate the safety of intranasal administration of NPY using a dose escalation, randomized, double-blinded, placebo-controlled crossover design in a medication-free, symptomatic PTSD group.

Inclusion Criteria:

• Men and women, age 18-60.
• Participants must have a level of understanding sufficient to agree to all tests and examinations required by the protocol and must sign a written informed consent document. We determine whether they have a sufficient understanding of the study procedures and risks by asking them to explain what's involved in the study and to give examples of study risks and benefits.
• Participants must fulfill DSM-IV criteria for current PTSD, based on the Structured Clinical Interview for DSM-IV Axis I Disorders (SCID-I) and on the Clinician-Administered PTSD Scale (CAPS).
• CAPS score must be at least 40 (moderate PTSD severity) at screening.

Exclusion Criteria:

• Current, primary Axis I disorders other than PTSD.
• History or current bipolar disorder or primary psychotic disorders (e.g. schizophrenia, schizoaffective disorder).
• Current diagnosis of anorexia nervosa or bulimia nervosa.
• Women who are pregnant or are breast-feeding.
• Drug or alcohol abuse or dependence within the preceding 3 months.
• poorly controlled hypertension (manifest by SBP > 140 and/or DBP > 90); HR < 60 or > 100 at rest at the time of screening and confirmed immediately prior to randomization
• Evidence of coronary artery disease as evidenced by history, abnormal ECG, typical symptoms
• History of arrhythmia, cardiac surgery, or family history of sudden death
• Hepatic dysfunction as defined by AST and ALT > 2x URL, or alkaline phosphatase and bilirubin > 1.5 x URL within X days prior to randomization
• Chronic renal disease as defined by serum creatinine > 1.9
• Any other serious or unstable clinically significant abnormal findings of laboratory parameters, physical examination, or ECG as determined by the PI.
• Any other serious or unstable condition that would put the subjects at undue risk as determined by the PI or additional safety monitor.
• Serious and imminent suicidal or homicidal risk.
• Psychotropic medication that will not be tapered off at least 7 days prior to screening; withdrawal symptoms must be absent at the time of screening
• History of nasal disorders or sinonasal surgery, or significant nasal abnormalities based on nasal exam.
• Received investigational intervention within 30 days prior to randomization