Prazosin is a selective alpha-1 adrenergic receptor antagonist used in the treatment of hypertension (high blood pressure) and benign prostatic hyperplasia (BPH) (growth of the prostate). It may be used for the management of nightmares and sleep disturbances associated with post-traumatic stress disorder (PTSD). It works by blocking alpha-1 receptors on vascular smooth muscle, causing vasodilation (widening of blood vessels) and lowering blood pressure. It also reduces urinary obstruction in BPH by blocking receptors on the smooth muscle of the bladder neck and prostate. Prazosin also crosses the blood-brain barrier, where it regulates noradrenergic activity involved in PTSD-related nightmares.

Alpha-1 receptors are found in blood vessels of the skin, kidneys, digestive organs, brain, prostate, ureters and eye muscles. These receptors can tighten the blood vessels (vasoconstriction) and increase blood pressure.

Prazosin is a selective alpha-1 adrenergic receptor antagonist that selectively blocks alpha-1 receptors, thus helping manage hypertension, benign prostatic hyperplasia and sleep disturbances associated with PTSD.

It does not block alpha-2 receptors, thereby avoiding the reflex tachycardia (rapid heart rate due to sudden drop in blood pressure) caused by unchecked noradrenaline release.

Prazosin has also been studied for Raynaud's phenomenon and PTSD-related nightmares. These should only be considered under specialist medical supervision.

Hypertension

In resistant hypertension, when other agents are not tolerated.

Benign prostatic hyperplasia (BPH)

Relieves urinary symptoms such as slowness or pain while peeing, difficulty urinating, incontinence, and inability to completely empty your bladder.

PTSD-associated nightmares and sleep disturbance

When medication is given at bedtime.

Pheochromocytoma

o prevent hypertensive crises during an operation.

Raynaud's phenomenon

Helps reduce vasospasm (constriction of blood vessels).

• Effective blood pressure reduction without reflex tachycardia.

• Improves urinary symptoms in BPH and lowers blood pressure simultaneously.

• Improves insulin sensitivity, potentially benefiting patients with metabolic syndrome.

• Effective for PTSD-related nightmares.

• Generic and widely available.

• Does not cause bronchoconstriction, making it suitable for patients with asthma or COPD.

Common

• Dizziness, especially upon standing (orthostatic hypotension)

• Headache, drowsiness, fatigue

• Palpitations (pounding heart)

• Nasal congestion

• Nausea

• Dry mouth

• Weakness, lack of energy

Uncommon

• Peripheral oedema (swelling due to fluid buildup)

• Reduced urinary frequency or incontinence

• Blurred vision

• Skin rash, itching

Serious side effects requiring immediate attention

• First-dose syncope (temporary loss of consciousness) or severe orthostatic hypotension

• Priapism (prolonged painful erection for more than 4 hours)

Intraoperative floppy iris syndrome (during cataract surgery)

• Severe allergic reactions & angioedema (swelling of tissues under the skin

• Severe tachyarrhythmias (fast & irregular heart rhythm

Take Prazosin orally exactly as prescribed. The first dose is small and usually recommended at bedtime to reduce the risk of first-dose syncope. The dose is gradually titrated every few days upwards based on response, with a usual maintenance dose. Swallow capsules whole with water. It can be taken with or without food. Avoid driving for the first 24 hours after the first dose or after a dose increase. Do not stop Prazosin suddenly without consulting your doctor, as gradual reduction (titration) is preferred where possible.

Prazosin is a competitive, selective antagonist of alpha-1 adrenergic receptors. Alpha-1 receptors are located on the smooth muscle of arterioles, veins, the bladder neck, the prostate, and many other tissues. When activated by noradrenaline, alpha-1 receptors trigger smooth muscle contraction, narrowing blood vessels (raising blood pressure) and constricting the bladder neck and prostate (causing urinary obstruction in BPH).

By selectively blocking alpha-1 receptors, prazosin causes vasodilation of both arteries and veins, reducing peripheral vascular resistance and venous return, thereby lowering both systolic and diastolic blood pressure. Since prazosin does not block alpha-2 receptors, the negative feedback that normally limits noradrenaline release remains intact, avoiding the reflex tachycardia seen with non-selective alpha-blockers.

In BPH, prazosin relaxes the smooth muscle of the bladder neck and prostatic urethra, reducing the dynamic component of bladder outlet obstruction, thereby improving urinary flow. Although it does not shrink the prostate, it provides rapid symptom relief, often within days.

In PTSD, prazosin crosses the blood-brain barrier and blocks alpha-1 receptors associated with arousal, fear processing, and REM sleep (deep sleep). By dampening the heightened noradrenergic tone seen in PTSD, prazosin reduces nightmares, hyperarousal, and sleep disturbance.

• Food (NIL): Can be taken with or without food.

• Alcohol (MODERATE): Increases risk of orthostatic hypotension and dizziness. Limit intake.

• Salt-restricted diet (BENEFICIAL): Supports the anti-hypertensive effect.

• Caffeine (MILD): May counteract sedation.

PDE-5 inhibitors (sildenafil, tadalafil, vardenafil)

SEVERE

Severe hypotension. Separate by at least 4–6 hours.

Other antihypertensives (ACE inhibitors, ARBs, beta-blockers, diuretics)

MODERATE

Additional blood pressure lowering. Start Prazosin at a lower dose & titrate cautiously.

Beta-blockers

MODERATE

Additional hypotension, especially orthostatic. Monitor BP closely.

NSAIDs

MODERATE

May reduce the antihypertensive effect. Monitor BP.

Tricyclic antidepressants

MODERATE

Additional orthostatic hypotension.

Other alpha-blockers (tamsulosin, doxazosin, alfuzosin)

SEVERE

Additional hypotension. Avoid concurrent use.

Verapamil and diltiazem

MODERATE

Risk of additive hypotension.

CNS depressants (alcohol, sedatives)

MODERATE

Additional sedation and dizziness.

• Severe heart failure or aortic stenosis (CAUTION): Risk of severe hypotension (low blood pressure).

• Hepatic impairment (CAUTION): Clearance may be hampered, hence lower doses are required.

• Volume depletion (CAUTION): Increased first-dose hypotension risk.

• Cataracts (CAUTION): Inform your doctor about the use of this medication to reduce the risk of floppy iris syndrome.

• Pheochromocytoma (CAUTION): Avoid beta-blocker monotherapy until alpha-blockade is established.

• Severe coronary artery disease (CAUTION): Risk of angina from reflex tachycardia.

Overdose of prazosin may result in severe hypotension, rapid heart rate, drowsiness, weakness, and, in some severe cases, even shock. Management of an overdose may involve laying the patient flat with legs raised, giving intravenous fluids for hypotension, and using a vasopressor (such as noradrenaline) if needed. Note that adrenaline is contraindicated as it can paradoxically worsen hypotension by stimulating unblocked beta receptors. Continuous cardiac and blood pressure monitoring is required. Activated charcoal may be considered for recent ingestions.

Take a missed dose as soon as you remember, unless it is close to the time of the next dose. In such a case, skip it and continue with your normal schedule. Do not double-dose. If you miss several doses or stop for more than a few days, contact your doctor before resuming, as you may need to restart at a lower dose to avoid a recurrence of the first-dose phenomenon.