Prazosin — what it does and how to use it safely

Ever felt dizzy after standing up too fast? That sudden drop in blood pressure is exactly what prazosin can cause — and why people need to be careful. Prazosin is an alpha-1 blocker most often used for high blood pressure and, off-label, for nightmares linked to PTSD. It helps relax blood vessels so blood flows easier, but that relaxation is exactly why the first few doses can hit hard.

If your doctor prescribed prazosin, you'll probably start on a very low dose at bedtime. Why bedtime? The first-dose or early-dose drop in blood pressure is common, and taking it at night reduces the risk of fainting during daily activities. Most people notice improved symptoms within days to weeks for blood pressure and a few weeks for sleep-related PTSD symptoms, but everyone responds differently.

What to expect — common effects and things to watch for

Common side effects are dizziness, lightheadedness, drowsiness, headache, and nasal congestion. Those first-dose fainting spells are real — stand up slowly and sit down if you feel lightheaded. If you’re taking other blood pressure meds, diuretics, or drugs like sildenafil (Viagra), your risk of low blood pressure goes up. Avoid alcohol until you know how prazosin affects you; alcohol can make dizziness worse.

Less common but serious signs include fainting that won’t stop, extremely low blood pressure, fast or irregular heartbeat, and severe swelling. If you get chest pain, trouble breathing, or a fainting spell, seek medical help right away.

Practical tips for taking prazosin

Take prazosin exactly as your doctor tells you. Don’t double up if you miss a dose; take the next dose at the usual time. Stand up slowly from sitting or lying down to reduce dizziness. If your doctor plans to raise the dose, they’ll usually do it slowly over days or weeks — this helps your body adjust.

Track your blood pressure at home if possible, especially in the first few weeks or whenever your dose changes. Keep a list of all medications, including supplements, and show it to your prescriber — some combinations increase the risk of low blood pressure. Tell your doctor if you’re pregnant, planning pregnancy, or breastfeeding.

Curious if prazosin is right for PTSD-related nightmares? Small clinical trials and clinical experience suggest it can help reduce nightmare frequency and improve sleep for some people, but it’s not guaranteed and isn’t the right choice for everyone. Talk with a clinician who knows both PTSD care and medication management to weigh pros and cons.

Bottom line: prazosin can work well for certain blood pressure and sleep symptoms, but it needs careful dosing and attention to side effects. Ask questions, monitor your blood pressure, and report anything worrying to your healthcare provider.