Prazosin can occasionally cause sudden fainting after the first dose and anytime that your dose is increased. To reduce your risk of fainting, the first dose prescribed by your doctor will be the smallest dose available. You should take this first dose as you are going to bed. This will decrease the possibility of fainting. Your dose may be gradually increased. Take your first new dose at bedtime when your dose is increased unless directed otherwise by your doctor.
Use this medication regularly in order to get the most benefit from it. To help you remember, take it at the same time(s) each day. If you are taking this medication for high blood pressure, keep taking it even if you feel well. Most people with do not feel sick. It may take up to several weeks before the full benefit of this drug takes effect.