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Summary: Prazosin is a medication originally used to help with high blood pressure, but can also be used for symptoms of severe stress, trauma and post-traumatic stress disorder (PTSD) such as sleep and nightmares.
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What Is It Used For?

Prazosin is used for many conditions including:

  • Cardiovascular conditions such as high blood pressure and Reynaud’s phenomenon;
  • Sleep problems such as nightmares, especially if due to an overactive “fight/flight” system from stress, anxiety or trauma (such as post-traumatic stress disorder).

What is the Evidence?

Studies suggest that prazosin can be helpful for the hyperarousal seen with nightmares seen with adults with PTSD ((Taylor, 2008; Raskind, 2013; Ahmadpanah, 2014).

Other studies suggest it may also be helpful for children and youth as well (Akinsanya, 2017).

How Does It Work?

Prazosin is in a class of medications called alpha-blockers (specifically, an alpha-1 adrenoceptor antagonist).

In conditions such as anxiety and PTSD, the body’s alarm becomes turned on, leading to a state of “sympathetic” activation -- like a fire alarm that turns on but fails to turn off.

Prazosin blocks some of this excessive activation in order to help with nightmares and sleep, and may also help with other symptoms such as flashbacks, being startled easily, and irritability or anger.

How To Use

How is it taken?

  • It is usually taken by mouth, with or without food.

What dosage?

  • You usually start at a low dose and increase to a higher dose that works for you.

When to take it?

  • When taken for sleep and insomnia, it is usually taken one hour before bedtime.
  • Note that the first dose might make you feel a bit dizzy or faint; if so, then just get into bed earlier that day.
  • It is always best to try to take it at the same time each day, which helps you remember and helps your body adjust to it.

What is a Usual Dosage?

Availability in Canada: 1, 2, 5 mg tablets.

For adults (aged 16+)

  • Start at 1 mg bedtime
  • Monitor for low blood pressure after the first dosage.
  • Gradually increase to 2-6 mg at bedtime.
  • Studies of military patients have used higher dosages (e.g. 10-16 mg bedtime).

For youth (Keeshin, 2017).

  • Start at 1 mg nightly and titrated, gradually, to 2–3 mg QHS depending on clinical response over the first 2 weeks.

When Will It Start Working?

When used for blood pressure, prazosin works within hours. When used for sleep or nightmares, improvements are usually noticed by five days or so (Consumer Reports, 2011).

How Long Do I Have to Take It?

When taken for sleep and nightmares, usually at least several weeks to months.

Is It Addictive?

Prazosin is not addictive. People do not get “cravings” for this medication like they might with nicotine or street drugs. If you and your doctor decide it is best for you to stop taking this medication, your doctor will explain how to safely come off this medication so you don’t feel negative effects as your body adjusts to being without it.

What About Side Effects?

Side effects are more likely during the first week of treatment or after an increase in dose.

Common side effects are

  • Lightheadedness
  • Dizziness,
  • Daytime sedation,
  • Fatigue or
  • Headache

Prazosin can cause low blood pressure -- in fact, the original use for prazosin was to treat high blood pressure.

What can I do If I feel lightheaded or dizzy?

  • Take caution when you are getting out of bed in the morning and when you are going up and downstairs. Changing your position more slowly from sitting to standing will help to prevent lightheadedness, dizziness and feeling like you might faint or pass out.
  • Drink plenty of fluids and avoid dehydration. Try to drink at least 2 L of water per day especially during periods of hot weather and when you exercise.
  • Avoid drinking excessive caffeine. Avoid more than the equivalent of 2 cups of coffee, tea or cola per day as this may you to urinate more, leading to dehydration; too much caffeine can also worsen sleep, anxiety and irritability. Avoid energy drinks as only one energy drink may contain the equivalent of 2-4 cups of coffee.

Side effects are generally mild and go away with time as you get used to the medication.

Are side effects severe or persistent, such as the following:

  • Feeling faint or lightheaded, rapid heartbeat, like your heart is pounding, or has skipped a beat or if you feel short of breath.

If so, then let your prescriber know. They can monitor your blood pressure, or recommend increasing at a slower rate, decreasing or stopping the medication.

Any Precautions With This Medication?

Tell your doctor or pharmacist if you:

  • Have any allergies, or have experienced a reaction to a medication
  • Are taking, or plan to start taking any other prescription or non-prescription medications (including herbal products), as there may be medication interactions.
  • Have any other medical conditions, especially high or low blood pressure, heart disease, and diabetes.
  • Miss a period, are pregnant (or are planning to become pregnant) or are breastfeeding. Tell your doctor if you become pregnant while taking this medication.
  • Are currently using alcohol or street drugs. These substances may interfere with how well this medication works for you and/or make you feel drowsy.

Has the dose been adjusted to the effective dose that is best tolerated?

  • Do not stop taking prazosin suddenly, as this can cause symptoms to “rebound”.
  • When it is time to stop the treatment, your doctor will decrease the dose gradually and monitor your systems.

Notice any allergy symptoms such as skin rash or hives, shortness of breath, itching, swelling, and cough?

  • If so, then stop taking this medication and let your prescriber know.

What If I Forget a Dose?

Did you miss a dose? If so, then just go back to your usual dose and usual time the next time you are scheduled to have a dose.

How Is It Stored?

Keep this medication in the original container, stored at room temperature away from  moisture and heat (e.g. not in the bathroom or kitchen) and protected from light.

Keep this medication out of reach and sight of children.


Akinsanya A, Marwaha R, Tampi RR. Prazosin in Children and Adolescents With Posttraumatic Stress Disorder Who Have Nightmares: A Systematic Review. J Clin Psychopharmacol. 2017 Feb;37(1):84-88. doi: 10.1097/JCP.0000000000000638. PMID: 27930498.

Ahmadpanah M, Sabzeiee P, Hosseini SM, Torabian S, Haghighi M, Jahangard L, et al. Comparing the effect of prazosin and hydroxyzine on sleep quality in patients suffering from posttraumatic stress disorder. Neuropsychobiology (2014) 69:235–42. doi: 10.1159/000362243

Prazosin for post-traumatic stress disorder, Consumer Reports, Updated Aug 2011. Retrieved Dec 31, 2020 from

Raskind MA, Peterson K, Williams T, Hoff DJ, Hart K, Holmes H, et al. A trial of prazosin for combat trauma PTSD with nightmares in active-duty soldiers returned from Iraq and Afghanistan. Am J Psychiatry (2013) 170:1003–10.


Raskind M et al.: Higher Pretreatment Blood Pressure Is Associated With Greater Posttraumatic Stress Disorder Symptom Reduction in Soldiers Treated With Prazosin, Biological Psychiatry, 2016 Nov 15, 80(10): 736-742.


Taylor FB, Martin P, Thompson C, Williams J, Mellman TA, Gross C, et al. Prazosin effects on objective sleep measures and clinical symptoms in civilian trauma posttraumatic stress disorder: a placebo-controlled study. Biol Psychiatry (2008) 63:629–32. doi: 10.1016/j.biopsych.2007.07.001

About this Document

Written by the health professionals at CHEO, including Marla Sullivan, Pharmacist and Helen Spenser, Psychiatrist.

Creative Commons License

You are free to copy and distribute this material unchanged and in its entirety as long as 1) this material is not used in any way that suggests we endorse you or your use of the material, 2) this material is not used for commercial purposes (non-commercial), 3) this material is not altered in any way (no derivative works). View full license at For any other uses, please contact the original rights holder, the Kelty Mental Health Centre.


Information in this pamphlet is offered ‘as is' and is meant only to provide general information that supplements, but does not replace the information from your health provider. Always contact a qualified health professional for further information in your specific situation or circumstance.

Date Posted: Jan 1, 2021
Date of Last Revision: Nov 18, 2021

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