Prazosin, sold under the brand name Minipress among others, is a medication used to treat high blood pressure, symptoms of an enlarged prostate, and nightmares related to post-traumatic stress disorder (PTSD).

The antihypertensive characteristics of prazosin make it a second-line choice for the treatment of high blood pressure.

[11] During its use for urinary hesitancy in military veterans in the 1990s, Murray A. Raskind and colleagues discovered that prazosin appeared to be effective in reducing nightmares.

Subsequent reviews indicate prazosin is effective in improving sleep quality and treating nightmares related to post-traumatic stress disorder (PTSD).

[18][19][20] Common (4–10% frequency) side effects of prazosin include dizziness, headache, drowsiness, fatigue, weakness, palpitations, and nausea.

[3] Less frequent (1–4%) side effects include vomiting, diarrhea, constipation, edema, orthostatic hypotension, dyspnea, syncope, vertigo, depression, anxiety, nasal congestion, and rash.

[3][21] One phenomenon associated with prazosin is known as the "first-dose response", in which the side effects of the drug — specifically orthostatic hypotension, dizziness, and drowsiness — are especially pronounced in the first dose.

[3] Orthostatic hypotension and syncope are associated with the body's poor ability to control blood pressure without active α-adrenergic receptors.

[28] α1-Adrenergic receptors have additionally been found on immune cells, where catecholamine binding can stimulate and enhance cytokine production.