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Prazosin (Minipress®)

Prazosin (Minipress® and generic forms) belongs to a group of medications called “alpha-1 receptor blockers.”

What is this medication used for?

Prazosin is not approved by Health Canada for use in children and adolescents.

However, when potential benefits outweigh risks, prazosin may be prescribed “off-label” for the treatment of nightmares associated with post- traumatic stress disorder (PTSD), hypertension, and Raynaud’s phenomenon (temporary discoloration of fingers/toes in cold environments) in children and adolescents. Learn more about off-label medication use:

Tell your doctor or pharmacist if you:

  • Have allergies or bad reactions to a medication
  • Take (or plan to take) other prescription or non-prescription medications, including natural medicines. Some medications interact with prazosin. Your doctor may adjust medication doses or monitor for side effects
  • Have a history of diabetes, kidney disease or psychiatric conditions such as depression or bipolar disorder
  • Miss a menstrual period, are pregnant, breastfeeding or planning a pregnancy
  • Use alcohol or drugs. Taking prazosin together with certain substances may cause a bad reaction. Learn more at

When will the medication start to work?

Some improvements may be seen within 1 to 2 weeks of starting prazosin. It can take up to 8 weeks to see the full benefits. When prazosin is working well, you may notice a reduction of nightmares and improved sleep.

It is important that you continue taking prazosin regularly, even if you are feeling well or there are no improvements in the first few weeks. Talk with your doctor if you feel that prazosin has not been helpful or if side effects are too bothersome. Your doctor may recommend switching you to a different medication.

This medication is not addictive. Do not stop taking it before talking to your doctor.

Possible common or serious side effects:

Side effects may be more common when starting a medication or after a dose increase. Talk to your doctor, nurse or pharmacist if any side effect concerns you.

  • Dizziness, lightheadedness or drowsiness
  • Low blood pressure
  • Headache
  • Nausea

Contact your doctor immediately if you experience:

  • Fainting, feeling lightheaded or difficulty with balance
  • Blurred vision or eye pain
  • Fast, slow or irregular heartbeat
  • Muscle weakness or decreased energy
  • Skin rash with swelling and itching or trouble breathing
  • Swelling in any area of the body
  • Sadness, depression or unusual changes in mood
  • Prolonged (more than four hours), inappropriate, and/or painful erection of the penis

How do I take this medication?

For treatment of PTSD-associated nightmares and sleep disturbances, prazosin is usually taken once daily just before bedtime. It can be taken with or without food. Prazosin needs to be taken regularly on a daily basis to be effective. Usually, you will start with a low dose and slowly increase this dose over several days or weeks, based on how you tolerate it.

Prazosin is available in tablets that are taken by mouth. If necessary, tablets may be broken in half, but they should not be crushed or chewed.

What precautions should my doctor and I be aware of when taking this medication?

  • Many medications may interact with prazosin, including alpha-agonists, beta-agonists, antipsychotics, sleep aides, beta-blockers, calcium channel blockers and several other medications. If you are (or begin) taking any other prescription, over-the counter medication, natural health product or supplement, check with your doctor or pharmacist to see if they are safe to use.
  • When taking this medication, it is important to drink enough liquids to prevent dehydration. Limit your intake of caffeine-containing products (such as coffee, black/ green tea, soft drinks and energy drinks), and replace fluids lost due to excessive sweating from work or exercise.
  • While taking this medication, if you feel dizzy, drowsy or slowed down, do not drive a car or operate heavy machinery. Alcohol could make this worse. Try to avoid alcohol while taking prazosin.

What special instructions should I follow while using this medication?

  • Keep all appointments with your doctor. Your doctor may order certain tests to check how you are responding and monitor for side effects.
  • Do not allow anyone else to use your medication.

What should I do if I forget to take a dose of this medication?

If you take prazosin regularly and forget to take a dose, skip the missed dose and take your next dose at its regularly scheduled time the next day. DO NOT double your next dose to try to ‘catch up’.

If you take prazosin on a different schedule than once daily at bedtime, talk with your doctor about what to do if you forget to take a dose.

How do I store this medication?

Keep this medication in the original container, stored at room temperature away from moisture and heat and protected from light. Keep this medication out of reach and sight of children.

How does this medication work?

Prazosin affects actions of the brain chemical norepinephrine (noradrenaline). Norepinephrine influences blood pressure, heart rate, and anxiety in the body, but it also affects sleep and arousal. This medication stabilizes certain areas of the brain, making them “less excited.” This improves symptoms of PTSD, such as nightmares and sleep disturbances.

How well does the medication work in children and adolescents?

Prazosin has been shown to be better than placebo (an inactive pill) for the treatment of PTSD-related nightmares and sleep disturbances in adults. Less information is available on the use of prazosin for treating PTSD-related nightmares in children and adolescents, but the available evidence is supportive.

Prazosin does not cure or treat other symptoms of PTSD. Prazosin may be used in combination with antidepressants (for example, selective serotonin reuptake inhibitors (SSRIs) or tricyclic antidepressants (TCAs) for the treatment of PTSD). The addition of trauma-focused cognitive behavioural therapy (CBT) may help increase the potential for benefit.

How long should I take the medication for?

This depends on the symptoms you have, how frequently they occur, and how long you have had them. Your doctor will discuss the benefits and risks of taking prazosin with you. At this time, you can also discuss how long you might need to take this medication.

Do not increase, decrease, or stop taking this medication without discussing it with your doctor. If you stop taking the medication suddenly, it is possible that your symptoms may return or you may have a bad reaction.

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