Prazosin is used to reduce high blood pressure. Learn how to use the medication, its common side effects, special precautions to watch out for, and more.

What is this medication for?

Prazosin belongs to a group of medications known as alpha-1 blockers. It is used to reduce high blood pressure in people with hypertension. It works by widening (relaxing) blood vessel walls thus lowering your blood pressure. 

This medication may also be used for other conditions. Check with your healthcare professional if you are unsure why you are given this medication.

How should I take or use this medication?

• Do not stop taking your medication without checking with your healthcare professional.
• You may take this medication with or without food. 

What should I do if I forget to take or use this medication?

If you forget to take a dose, take it as soon as you remember. Then take your next dose at the usual time. Do not take two doses to make up for the missed dose. 

What precautions should I take when taking or using this medication?

Inform your healthcare professional if: 

• You are allergic to this medication or any of the other ingredients of this medication.
• You are pregnant, planning to become pregnant, or breastfeeding
• You have heart problems (e.g. chest pain / angina)
• You have kidney problems
• You are undergoing eye surgery for cataracts (cloudiness of the lens). Inform your eye specialist before the operation that you are currently taking or have previously taken the medication. The pupil may dilate poorly and the iris (the coloured part of the eye) may become floppy during the operation. It is important to inform the eye specialist on this as the operation may need to be carried out differently. 

What are some common side effects of this medication?

• Dizziness, light-headedness or fainting 
  • These side effects may occur, especially when you are taking Prazosin for the first time, restarting treatment, or taking a higher dose of Prazosin. These may also occur when you stand up quickly from a lying or sitting position. If you are affected by this, you should lie down until you feel better then sit for a few minutes before standing again to prevent these effects from returning. These side effects usually improve with time once you have become used to taking this medication.
• Drowsiness 
  • May affect your level of focus or ability to drive and use machinery. Make sure that you are not feeling drowsy before you drive or do things that require you to be alert.

What are some rare but serious side-effects that I need to seek medical advice immediately?

The symptoms of a drug allergy include one or more of the following: 

• Swollen face/eyes/lips/tongue
• Difficulty in breathing
• Itchy skin rashes over your whole body

If you experience any of these symptoms, you should stop your medication and see your healthcare professional immediately.

What food or medication should I avoid when I take or use this medication?

Avoid drinking alcohol as it may increase the risk of dizziness, light-headedness or drowsiness. 

This medication may interact with other medications. 

Examples include: 

• Sildenafil, Tadalafil or Vardenafil

Inform your healthcare professional of any other medications that you are currently taking and consult them if you are unsure whether your existing medications can be taken together with Prazosin.

How should I store this medication?

Store in a cool and dry place, away from direct sunlight. Keep this medication away from children. 

How do I throw away this medication safely?

Pack this medication into a black trash bag and seal it tightly before throwing into the rubbish chute or bin. 

Disclaimer

Please take note that the above is not a complete list of all possible side effects. If you have any concerns about your medication or if you have other side effects that you think are caused by this medication, please consult your doctor or pharmacist.

If you take more than the recommended dose, please seek medical advice immediately. The information provided on this page does not replace information from your healthcare professional. Please consult your healthcare professional for more information.

This article is jointly developed by members of the National Medication Information workgroup. The workgroup consists of cluster partners (National Healthcare Group, National University Health System and SingHealth), community pharmacies (Guardian, Unity and Watsons) and Pharmaceutical Society of Singapore. The content does not reflect drug availability and supply information in pharmacies and healthcare institutions. You are advised to check with the respective institutions for such information.

Last updated on April 2025