Stephanie Howe, DVM
By Stephanie Howe, DVM on Apr. 21, 2023

In This Article


PetMD’s medications content was written and reviewed by veterinary professionals to answer your most common questions about how medications function, their side effects, and what species they are prescribed for. This content shouldn’t take the place of advice by your vet.

What Is Prazosin?

Prazosin has been commonly used in the treatment of urinary tract obstructions in cats, but recent studies have shown that it may not be as effective as once thought in the treatment of this condition.  

Prazosin may also be used as part of a multidrug treatment plan to help with several medical issues including high blood pressure in dogs and cats and congestive heart failure (CHF) in dogs.

Prazosin is FDA-approved for human use under the brand name Minipress® and the generic prazosin. Prazosin is currently not FDA-approved as a veterinary medication. However, it is readily utilized in the veterinary field, and veterinarians can legally prescribe certain human drugs in animals in certain circumstances. This is called extra-label or off-label use because this use isn’t described on the drug label.

How Prazosin Works

Prazosin belongs to a class of medications called alpha-1 adrenergic blockers. Prazosin blocks alpha-1 receptors located on the veins and arteries, causing them to relax and dilate (widen). This dilation creates more space within the veins and arteries for blood to flow, thereby lowering the body’s overall blood pressure.

In pets with urinary tract obstructions, prazosin relaxes the muscles of the urethra that may be spasming due to the obstruction. It can also dilate (widen) the urethral sphincter to allow for easier urination.

In certain circumstances, your vet may recommend a compounded formulation of prazosin. Compounded medications are prescribed if there’s a specific reason your pet’s health can’t be managed by an FDA-approved drug, such as if your pet has trouble taking pills in capsule form, the dosage strength is not commercially available, or the pet is allergic to an ingredient in the FDA-approved medication. Compounded medications are not FDA-approved. They are created by either a veterinarian or a licensed pharmacist on an individual basis to best suit a patient’s particular needs. You can learn more about compounded medications here.

Prazosin Directions

Follow the directions on the drug label or as provided by your veterinarian. Prazosin can be given with or without food, but if your pet experiences an upset stomach after taking this medication on an empty stomach, try offering prazosin with a small meal or treat.

Dosages for this medication vary depending on the species and the disease process being treated. This medication may be given once daily or up to three times daily. Follow your veterinarian’s recommendations for your specific pet.

Missed a Dose?

Speak with your veterinarian about what to do if you forget to give a dose of prazosin. Generally, they may instruct you to give it when you remember or, if it is almost time for your next dose, to skip the missed dose and resume your normal dosing schedule. Do not give extra or double doses.

Prazosin Possible Side Effects

  • Abnormally low blood pressure or fainting
  • Lethargy

  • Weakness

  • Dizziness

  • Vomiting

  • Diarrhea

  • Constipation

  • Elevated third eyelid

Human Side Effects

Prazosin is also a prescription medication for humans, frequently with dosages different from those prescribed for your pet by a veterinarian. Due to possible side effects, pets should not be given any medicine prescribed for humans. If you accidentally ingest a pet medication, call your physician or the national Poison Control Center hotline at 800-222-1222.  


Specific monitoring or routine testing while your pet is on this medication may be recommended by your veterinarian depending on your pet’s individual needs, other medications they may be on, and/or the issue that initially caused your pet to be placed on this medication.

Call Your Vet If:

  • Severe side effects are seen (see above)

  • Your pet’s condition worsens or does not improve with treatment

  • You see or suspect an overdose

  • You have additional questions or concerns about the use of prazosin

Prazosin Overdose Information

Signs of an overdose of prazosin may include incoordination, dizziness, lethargy, low blood pressure, trembling, elevated heart rate, and loss of consciousness.

If you suspect an overdose, immediately contact your veterinarian, seek emergency veterinary care, or contact an animal poison control center. Consultation fees often apply.

Pet Poison Helpline (855) 764-7661

ASPCA Animal Poison Control (888) 426-4435

Prazosin Storage

Prazosin should be stored at controlled room temperatures from 68–77 F. Always confirm storage requirements by reading the label.

Keep the container tightly closed in order to protect from moisture and light.

Compounded medications should be stored according to the compounding pharmacy’s label.

Keep out of reach of children and pets.

Prazosin FAQs

How long does it take for prazosin to work in pets?

Prazosin starts working in your pet's body within the first few hours after administration.

No vet writer or qualified reviewer has received any compensation from the manufacturer of the medication as part of creating this article. All content contained in this article is sourced from public sources or the manufacturer.


Conway DS, Rozanski EA, Wayne AS. Prazosin administration increases the rate of recurrent urethral obstruction in cats: 388 cases. Journal of the American Veterinary Medical Association. 2022;260(S2): S7-S11.

Reineke EL, Thomas EK, Syring RS, Savini J, Drobatz KJ. The effect of prazosin on outcome in feline urethral obstruction. Journal of Veterinary Emergency and Critical Care (San Antonio). 2017;27(4):387-396

Acierno MJ, Brown S, Coleman AE, et al. ACVIM consensus statement: guidelines for the identification, evaluation, and management of systemic hypertension in dogs and cats. Journal of Veterinary Internal Medicine. 2018;32(6):1803-1822

Featured Image: Raymond


Stephanie Howe, DVM


Stephanie Howe, DVM


Dr. Stephanie Howe graduated from the University of Florida College of Veterinary Medicine in 2011, after receiving a Bachelor of Science...

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