9 Prazosin Side Effects and How to Manage Them

Prazosin (Minipress) is a prescription-only alpha blocker that helps manage high blood pressure. Some people take it by itself, while others turn to it for added support when other blood pressure medications aren’t doing enough. In other cases, it’s an off-label treatment for conditions like benign prostatic hyperplasia (BPH) and nightmares related to post-traumatic stress disorder (PTSD).

No matter the use, prazosin is fairly well-tolerated. But alpha blockers like prazosin aren't prescribed as often as other blood pressure medications. This is due to possible side effects. Most side effects are common and go away over time, but serious side effects can happen, too.

If you’re new to prazosin, it’s helpful to know what to expect. Below, we'll review what you should know about nine notable prazosin side effects and how to manage them.

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1. Dizziness

Dizziness is one of the most common prazosin side effects. Around 10% of people in prazosin’s initial studies reported it. You may also feel lightheaded or faint — especially when getting up too fast, exercising, or standing for long periods of time. This is because prazosin can cause a drop in blood pressure.

This side effect typically happens when first starting the medication, after raising your dose, or when another blood pressure medication is added to your treatment. The good news is you should feel less dizzy as your body gets used to the medication.

Managing dizziness

When you’re starting prazosin (or soon after a dose increase), you should be careful with driving and performing other tasks that need you to be alert. As your body gets used to prazosin, you can carefully resume these activities.

To help manage dizziness in the meantime, try taking your initial doses of prazosin in the evening. This can help limit the amount of daytime dizziness you feel. It's also ideal to minimize how much alcohol you drink while taking prazosin. Alcohol can cause dangerously low blood pressure when combined with prazosin and worsen dizziness.

If you're actively feeling dizzy or lightheaded, try to find a safe place to sit or lie down so you don't accidentally fall and hurt yourself. It also helps to get up slowly when you're going from sitting or lying down to standing.

Let your healthcare provider know if your dizziness becomes frequent or bothersome. This may be a sign that your blood pressure is too low. They may lower your dose or switch you to another medication.

2. Low blood pressure

Up to about 5% of people taking prazosin during clinical trials reported low blood pressure (hypotension). When your blood pressure is too low, you may experience dizziness, weakness, or lightheadedness. It may also cause you to faint.

Hypotension is more likely to happen when you first start taking prazosin. The risk is also higher if you have a history of hypotension, take more than one blood pressure medication, or take erectile dysfunction medications like Viagra (sildenafil).

Managing low blood pressure

Monitoring your blood pressure is key to managing it. Your healthcare provider will likely keep an eye on your blood pressure during your routine appointments. But it doesn’t have to stop there — you can also monitor it at home. Make sure to ask about your blood pressure goal so you know what readings to look for.

3. Headache

Headache is another common prazosin side effect. It was reported by about 8% of people in clinical trials. This side effect should also improve as your body gets used to the medication.

But, keep in mind that headaches could be caused by many things besides medication. These include not drinking enough water, consuming too much alcohol, and not getting enough sleep. Stress and certain health conditions can also cause headaches.

Managing headaches

You can try some free, quick things at home to manage headaches. This includes staying hydrated throughout the day and getting enough sleep. Routine exercise can also make a difference.

If headaches become hard to manage, ask your healthcare provider about over-the-counter (OTC) medications like acetaminophen (Tylenol) or ibuprofen (Advil, Motrin) for added relief. In some cases, your provider may also lower your prazosin dosage or switch you to a different blood pressure medication.

4. Drowsiness or lack of energy

About 8% of people taking prazosin report feeling drowsy (or sleepy). Having a general lack of energy is also possible when taking prazosin, but it’s less common.

Like dizziness and headaches, these side effects tend to happen when you’re starting the medication or after a dose increase. They should improve over time.

Managing drowsiness and lack of energy

When starting prazosin or changing your dose, you should minimize activities that need focus, like driving and intense exercise. It’s important not to drink alcohol or take other medications that make you feel sleepy (like opioids and sleep medications), if possible. These things can make you feel more tired and could increase the risk of accidents.

5. Weakness

Weakness is another common prazosin side effect. In clinical trials, about 7% of people taking prazosin felt weak at some point. This could be due to your blood pressure dropping too low.

Managing weakness

If you're feeling weak, try to find a safe place to sit or lie down so you don't accidentally fall and get hurt. You can also check your blood pressure to see if it’s too low.

Let your healthcare provider know if your blood pressure is dropping too low often or if your weakness becomes worse. You may need to switch to a different dose of prazosin or blood pressure medication altogether.

6. Nausea

Nausea is possible with prazosin. Thankfully, this side effect is usually temporary and short-lived.

Managing nausea

If you're feeling nauseous, a few things might help. This includes eating bland foods and remaining upright after eating. You can also try eating smaller, more frequent meals throughout the day. Larger, less frequent meals could add to stomach upset.

Let your healthcare provider know if your nausea doesn't go away or gets worse at any point. Prazosin isn’t the only possible cause of nausea, so they can help you figure out if prazosin is responsible for your symptoms.

7. Heart palpitations

Heart palpitations (irregular heartbeat) can happen with prazosin. Symptoms of heart palpitations can include a pounding or fluttering feeling in your chest.

These feelings in your chest could be a result of prazosin, another condition, or some combination of the two. Heart palpitations can be caused by many different things. Thyroid problems, anemia, and heart disease can cause heart palpitations. Stress, chronic lack of sleep, and caffeine also may trigger them.

Managing heart palpitations

Let your healthcare provider know if your palpitations last longer than a few minutes or start happening more often. You should get emergency care right away if they're accompanied by symptoms like chest, neck, or jaw pain, shortness of breath, or loss of consciousness. These added symptoms could be a sign of something more serious.

8. Priapism

Priapism (prolonged erection) is a rare but serious prazosin side effect. A prolonged erection is painful and typically lasts for more than 4 hours.

Managing priapism

Get emergency medical help right away if you have a painful erection that lasts longer than 4 hours. This isn’t something you should try to treat on your own — even if it’s an awkward subject to talk about. It can cause permanent damage to your penis if it’s not promptly treated.

9. Floppy iris syndrome

Prazosin can cause intraoperative floppy iris syndrome (IFIS), a problem that’s relevant during cataract surgery. This is a serious side effect that can raise your risk of eye problems during and after the surgery.

Let your eye provider know if you're taking prazosin and need eye surgery. They might need to adjust their surgical technique to prevent IFIS. It’s hard to manage IFIS on your own.

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Written by:

Nikki Javit, PharmD

Nikki Javit, PharmD, is a clinical pharmacist with certifications in international travel medicine, immunization delivery, and pharmacogenomics. She received her bachelor’s of science in biology from Indiana University Bloomington and her doctor of pharmacy degree from Butler University.

Edited by:

Joshua Murdock, PharmD, BCBBS

Joshua Murdock, PharmD, BCBBS, is a licensed pharmacist in Arizona, Colorado, and Rhode Island. He has worked in the pharmacy industry for more than 10 years and currently serves as a pharmacy editor for GoodRx.

Reviewed by:

Austin Ulrich, PharmD, BCACP

Austin Ulrich, PharmD, BCACP, is a board-certified ambulatory care clinical pharmacist. In his early career, he provided direct patient care in a variety of settings, including hospital and community pharmacies, and in a primary care clinic as a clinical pharmacist.

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