Blood pressure and eye tests may guide PTSD treatment

Copied word for word from the study's registry entry, so the wording is the study team's rather than ours.

Inclusion Criteria: * Veteran of the U.S. Armed Forces * Current diagnosis of PTSD (as documented in clinical chart and/or per participant report; a rule out diagnosis from a VA provider accompanied by a referral to the VA PTSD Outpatient Clinic (POC) will also be considered sufficient for inclusion) * Woman of childbearing potential must agree to abstain from sexual relations that could result in pregnancy or use an effective method of birth control acceptable to both participant and study clinician during the study. Men are not required to use contraception during the study. Exclusion Criteria: * Psychiatric: * Any known diagnosis of a primary psychotic or major neurocognitive disorder, including schizophrenia, brief psychotic disorder, or Alzheimer's or other dementia, as well as bipolar type I * Severe psychiatric instability or severe situational life crises, including evidence of being actively suicidal or homicidal, or any behavior which poses an immediate danger to participant or others. * Note: Nonsuicidal depression comorbid with PTSD will not be exclusionary. Participants may continue in any concurrent psychotherapy or pharmacotherapy in which they are participating, other than pharmacotherapeutic agents specifically listed above. Participants with active suicidal ideation or with depression severe enough to require psychiatric hospitalization will be excluded. * Medical: * Significant bilateral visual loss (would preclude performing the PLR measurements) * Current pregnancy or lactation * Allergy or previous adverse reaction to prazosin or other alpha-1 antagonist * Acute or unstable chronic medical illness, including unstable angina, recent myocardial infarction (within 6 months), congestive heart failure, preexisting hypotension (systolic \<110) or orthostatic hypotension (systolic drop \> 20mmHg after two minutes standing or any drop accompanied by dizziness); autoimmune disorders; insulin-dependent diabetes * Chronic renal or hepatic failure, acute pancreatitis, Meniere's disease, benign positional vertigo, or narcolepsy * Medication / treatment: * Any use within the 7 days prior to baseline of prazosin, doxazosin, clonidine, guanfacine, trazodone, or nonbenzodiazepine hypnotics, and/or unwillingness to avoid these medications for the duration of the study * Use of avanafil (Stendra), sildenafil (Viagra), tadalafil (Cialis), and vardenafil (Levitra) will be not be permitted during the study dose titration period because of increased risk of hypotension in combination with alpha-1 blockers, but will be allowed at 1/2 the usual starting dose following dose titration * Current use of nitrates, or of alternative medications or supplements with significant vasodilatory properties (e.g., nitrate containing supplements) * Participants may also be excluded at the discretion of PI or study clinicians if they appear to be unsuitable for this research study for a reason not detailed here.