Prazosin Starting Dose
The appropriate starting dose of prazosin is 1 mg at bedtime, regardless of indication. 1
FDA-Approved Dosing for Hypertension
The FDA drug label is explicit and unequivocal: patients should always be started on 1 mg capsules of prazosin 1. The 2 mg and 5 mg capsules are specifically not indicated for initial therapy 1. This recommendation stems from the critical safety concern of first-dose syncope, which occurs in approximately 1% of patients given an initial dose of 2 mg or greater 1.
- Initial dose: 1 mg two or three times daily for hypertension 1
- First-dose hypotension risk: Syncopal episodes typically occur within 30-90 minutes of the initial dose 1
- Safety monitoring: Patients should be cautioned to avoid situations where injury could result should syncope occur during initiation 1
The 2017 ACC/AHA Hypertension Guidelines consistently cite prazosin dosing as 2-20 mg daily in 2-3 divided doses for maintenance, but this reflects therapeutic ranges after appropriate titration from the 1 mg starting dose 2, 3, 4, 5.
Dosing for PTSD-Associated Nightmares
For PTSD nightmares, the evidence strongly supports the same conservative starting approach:
- Start at 1 mg at bedtime and increase by 1-2 mg every few days until effective dose is reached 6
- Average effective dose: Approximately 3 mg for civilian PTSD patients 6
- Higher doses for military veterans: Studies in combat veterans used mean doses of 9.5-13.3 mg/day, but still initiated at 1 mg 6, 7
- Civilian trauma victims: Mean dose of 3.1 mg ± 1.3 mg was effective 7
The 2010 Best Practice Guide for Nightmare Disorder provides Level A evidence that prazosin is recommended for PTSD-associated nightmares, with treatment generally started at 1 mg at bedtime 6.
Critical Safety Considerations
Orthostatic hypotension monitoring is mandatory, particularly after the first dose 6, 1. The risk of first-dose syncope can be minimized by:
- Limiting initial dose to 1 mg 1
- Slow subsequent dose increases 1
- Cautious introduction of any additional antihypertensive drugs 1
- Patient counseling about dizziness, lightheadedness, and fall risk 1
Special Populations
Elderly or debilitated patients: Consider even lower starting doses (0.25-0.5 mg) when treating hypertension, though this is not explicitly stated in guidelines for PTSD treatment 2.
Concurrent alpha-1 antagonists: Exercise extreme caution and use individualized titration with close monitoring if the patient is on other alpha-1 antagonists like carvedilol 8.
Titration Strategy
After the 1 mg starting dose is tolerated:
- For hypertension: Increase slowly to total daily dose of 6-15 mg in divided doses (usual therapeutic range), up to maximum 40 mg daily 1
- For PTSD nightmares: Increase by 1-2 mg every few days based on response and tolerability 6
- Monitor blood pressure at each dose increase, particularly in patients with cardiovascular risk factors 1
The evidence is unambiguous: 1 mg is the universal starting dose for prazosin across all indications, with careful upward titration based on response and tolerability while monitoring for orthostatic hypotension.