Prazosin Side Effects

Estimated reading time: 33 minute(s)

High blood pressure, medically known as hypertension, is a condition in which the vessels within the body become narrow, making the blood flow faster. The condition, once acquired, is chronic and persists for a lifetime, putting a person at various risks, such as stroke. Hence, experts use different types of anti-hypertensive medications to ensure that the blood pressure in such individuals remains in control. 

Prazosin is one of these blood pressure-lowering medications commonly dispensed to millions of people across the world. Because it is a prescription medication, many people believe it is entirely safe to use without any risks. The reality is no medicine is completely risk-free, and many people have been reporting different Prazosin side effects despite taking it as recommended. The key is to be aware of these side effects and get help as soon as you think the situation is getting out of control.

A Rundown of Prazosin and How It Works

Prazosin is a prescription-only medication available in the form of oral capsules. It is often available under the brand name of Minipress in addition to various generic versions. The latter is more cost-effective than the brand versions but may not be available in all forms or strengths. Experts may prescribe Prazosin alone or in combination with other drugs to achieve adequate blood pressure control and avoid complications, such as stroke and heart attack.

Prazosin is a member of a drug class known as alpha-blockers. [1] It aims to decrease the high blood pressure in the body by relaxing the constricted blood vessels, allowing blood to pass through more easily and slowly. The medication must be taken consistently for the rest of the life to keep blood pressure under control unless advised by a doctor. Skipping it can diminish its effects, making a person hypertensive once again.

Common & Serious Prazosin Side Effects

People who are trying Prazosin capsules for the first time may experience drowsiness and dizziness following the first dose. Hence, experts always recommend them to abstain from performing any risky task or driving for the first 24 hours after taking it for the first time. The same dose applies to people whose doctors have recently increased the drug dose.

Additionally, Prazosin can also cause the following common side effects:[2] 

  • Dizziness
  • Lightheadedness
  • Drowsiness
  • Headache
  • Weakness
  • Lack of energy
  • Palpitations or a fluttery or racing heart
  • Nausea

Most of the side effects mentioned above are mild and likely to disappear within a few days or weeks. If they do not disappear or become severe, talk to a doctor or pharmacist.

Serious Side Effects

Very rarely, Prazosin may cause serious side effects for which a user may need to call emergency services, especially if they become life-threatening or a medical emergency. 

Following are some serious side effects of Prazosin to consider:[3]

  • Depression
  • Loss of consciousness (especially when standing up too quickly after lying down or sitting)
  • Depressed mood and thoughts
  • A very fast heartbeat
  • An erection lasting longer than four hours
  • Swelling of hands and feet
  • Allergic reactions leading to symptoms like skin rash, trouble breathing, facial swelling, and hives
  • Labored breathing

Prazosin Possible Interactions

An interaction is when a substance changes or alters the way a medication works, preventing the latter from being effective. Prazosin oral capsules can interact with other medications, herbs, or vitamins a person may already be taking. To avoid these interactions, a doctor must carefully scrutinize all drugs and ensure that none can affect how Prazosin works.

Following are some examples of drugs that can trigger interactions when taken with Prazosin:

Other Antihypertensive Drugs

People who combine Prazosin with other blood pressure-controlling medications may experience a significantly decreased BP, sometimes dangerously low. A doctor can help avoid this side effect by carefully regulating the dose of Prazosin or being cautious while adding another blood pressure with it. They may also keep a close eye on their blood pressure more frequently than usual. Some examples of standard blood pressure-lowering medications include the following:

  • Metoprolol
  • Losartan
  • Carvedilol
  • Atenolol
  • Valsartan
  • Amlodipine
  • Hydrochlorothiazide
  • Clonidine
  • Lisinopril

Drugs for Erectile Dysfunction

Many medications used to manage erectile dysfunction can often lower blood pressure simultaneously. Hence, combining any of these medications with prazosin can lead to a significant lowering of blood pressure, sometimes to a hazardous level. Some examples of drugs for erectile dysfunction treatment include sildenafil, avanafil, vardenafil, and tadalafil. Always remember to inform your doctor if you are taking any of these medications so that they can adjust the doses for Prazosin accordingly.

Important Prazosin Warnings to Remember

Keep the following warnings in mind if you are on Prazosin:

Warning for loss of consciousness

Because Prazosin lowers blood pressure, it may cause a user to faint, pass out, or suddenly lose consciousness, usually between 30 to 90 minutes following the first dose. The side effect may happen if your Prazosin dose was increased too quickly or another antihypertensive medication was added to your routine.

Warning for prolonged erections

In some people, Prazosin can cause prolonged erections, a condition known as priapism. If you get an erection that fails to go away after four hours, seek immediate emergency help at once, as priapism is a medical emergency and may cause tissue scarring or erectile dysfunction If not treated.

Warning for intraoperative floppy iris syndrome

People who suffer from cataracts and require surgery for their management may be at risk of complications during the procedure if they are already on Prazosin. One of these complications is known as intraoperative floppy iris syndrome (IFIS). Ensure that your doctor knows about your Prazosin use so that they can give you medications before the surgical procedure or adopt a different technique to prevent complications.

Allergy warning

In some people, Prazosin may trigger a severe allergic reaction with symptoms like hives, skin rash, trouble breathing, and swelling of the lips, tongue, and face. Call the nearest emergency room if you develop the symptoms of an allergic reaction, as it can quickly become life-threatening.

Alcohol interaction warning

Combining Prazosin with alcohol can make a person feel lightheaded, dizzy, or faint.

Warnings for people with pre-existing health conditions

People with the following pre-existing health issues must be cautious while using Prazosin:

  • Individuals with heart problems: Use Prazosin very cautiously if you have heart failure, swelling in your hands or feet, or a tendency to feel lightheaded or dizzy when you are standing up from a lying or sitting position (orthostatic hypotension). Additionally, Prazosin may also worsen a special type of chest pain called angina.
  • Individuals with eye problems: Prazosin can lead to eye pain and blurry vision. Hence, people with pre-existing vision problems may experience additional risks and complications while using Prazosin.

Warnings for certain groups

The following groups of people must be cautious when it comes to using Prazosin:

  • Pregnant women: Animal-based research has confirmed that Prazosin can cause harmful effects on the developing fetus when a pregnant female takes them. However, the proof of these damaging effects in human trials is limited. Speak to a doctor if you are planning to use Prazosin or have become pregnant while using the medication. A healthcare professional may compare the pros and cons to determine if it is safe to take Prazosin.
  • Breastfeeding mothers: Prazosin can pass onto breast milk and enter the baby’s body. Hence, consider talking to a doctor before taking it during breastfeeding.
  • For old-age groups: People above 65 years and taking Prazosin are at an increased risk of experiencing a sudden drop in blood pressure when they suddenly stand up from a lying or sitting position. The medication can also cause lightheadedness and dizziness. Hence, a doctor may start such people on a lower dosage and closely monitor their blood pressure. Alternatively, they may consider choosing a different drug altogether.
  • For children: The safety and efficacy of Prazosin in children remain unestablished.

How to Take Prazosin to Avoid Side Effects

Keep the following tips in mind to ensure that you take Prazosin effectively without exposing yourself to side effects:

  • Prazosin is a long-term medication that needs to be taken every day. A person may acquire serious harm if they do not take it as prescribed.
  • If you don’t take the medication or skip a dose, the blood pressure may continue to stay high, putting you at a high risk of serious health issues, such as stroke and heart attack.
  • If you miss doses or do not take Prazosin on schedule, it may become completely ineffective or reduce its therapeutic efficacy. For Prazosin to work optimally, a certain amount of this medication must always be present in the body.
  • Taking too much of this medication may cause a drop in blood pressure, leading to symptoms such as fainting, lightheadedness, extreme dizziness, shock, loss of consciousness, or fainting.
  • If you ever feel like you have taken too much Prazosin, call the doctor at once or seek help from the local poison control centers. Going to the nearest emergency room is recommended if the symptoms become too severe.
  • If you miss a dose of Prazosin, take it as soon as you remember. However, if the time for the next dose is only a few hours away, forget about the missed dose and carry on with the usual schedule to avoid doubling the medication. Never attempt to catch up by taking two tablets of Prazosin at once, as this may lead to a dangerous drop in blood pressure.
  • Always monitor your blood pressure while taking Prazosin. If the drug is working effectively, the blood pressure readings must be within normal limits.

Essential Considerations While Taking Prazosin

To minimize the chances of experiencing Prazosin side effects and to keep using it optimally, know the following tips:

General Considerations

  • Prazosin is available as oral capsules which can be opened as needed
  • Keep the medication away from moisture and light
  • Store it at room temperature between the temperatures of 68- and 77 degrees Fahrenheit.
  • Avoid storing Prazosin in damp, moist areas, such as bathrooms.

Considerations for Refills

All prescriptions for Prazosin are refillable, meaning an individual taking it may not require a new prescription each time they run out of it. A doctor writes the number of refills a person can avail of through a single prescription.

Travel Considerations

  • When you are traveling, always keep Prazosin with you in your carry-on bag to have it readily available in case of emergency.
  • You may need to show the medicine to airport security along with its pharmacy label. Hence, always carry it in its original container with a prescription label.
  • Avoid putting the medication in the glove compartment of the car. Avoid leading Prazosin in the car, especially in severe weather conditions, as they may change its composition and efficacy.


What will happen if I miss a dose of Prazosin?

Missing a dose of Prazosin can lead to very high blood pressure, putting a person at risk of stroke and heart attacks.

What should I avoid while I am on Prazosin?

Avoid engaging in any risky activity, such as driving, until you are sure about how this medication affects you. Some people may feel dizzy or lightheaded when they first start taking it. Avoid combining it with alcohol as it may exacerbate the side effects.

What kind of clinical monitoring is needed while I am on Prazosin?

A doctor may advise you to regularly check your blood pressure and heart rate to ensure the medication works effectively without any side effects.

Does Prazosin make you sleepy?

While Prazosin does not cause sleepiness, it may make a person lightheaded or drowsy due to low blood pressure.

How long do Prazosin side effects last?

The Prazosin side effects profile and duration can vary from one person to another. Most mild side effects settle on their own within a few days to weeks.

Is there a risk of Prazosin side effects weight loss?

Prazosin is not known to cause weight loss.


1 Basquez R, Pippin MM. Prazosin. [Updated 2023 Jan 23]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 Jan-. Available from:

2 “Minipress- prazosin hydrochloride capsule”. DailyMed. 23 July 2021. Retrieved 4 July 2023.

3 “Prazosin Hydrochloride Monograph for Professionals”. American Society of Health-System Pharmacists. Retrieved 4 July 2023.

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