Sildenafil (Viagra) for Dogs: A Medication to Lower Blood Pressure in the Lungs

Viagra is a well-known erectile dysfunction treatment for humans. Sildenafil, the active ingredient in Viagra, also treats pulmonary hypertension. Pulmonary hypertension is a condition that leads to high blood pressure in the lungs.

But what about sildenafil for dogs? It turns out that there are veterinary uses for sildenafil as a treatment for certain disorders in dogs, including canine pulmonary hypertension. 

Sildenafil (Viagra) for dogs at a glance

What is sildenafil (Viagra) for dogs and how does it work?

Sildenafil belongs to a class of medications called phosphodiesterase (PDE) inhibitors. These medications help dilate (expand) blood vessels and relax muscles in the body. Specifically, sildenafil is a PDE5 inhibitor that targets cells in the lungs and penis. 

PDE inhibitors work by blocking the enzyme phosphodiesterase. This helps lower the level of calcium inside your dog’s cells, resulting in benefits for certain conditions. 

What is sildenafil (Viagra) used for in dogs?

For dogs, sildenafil is primarily prescribed for two conditions: Pulmonary hypertension and megaesophagus.

Pulmonary hypertension

Sildenafil targets blood vessels in the lungs. The medication has been effectively used in dogs to treat pulmonary hypertension. Pulmonary hypertension is a life-threatening condition that occurs when blood pressure is too high in a dog’s lungs.

Pulmonary hypertension is usually the result of another health condition, such as heart disease. Therefore, treatment is aimed at lowering blood pressure in the lungs and managing the underlying condition, if possible.

Sildenafil is the only blood pressure medication thought to be effective at treating pulmonary hypertension in dogs. Other blood pressure medications do not specifically target blood vessels in the lungs like sildenafil does. And, in some cases, these other medications may make the problem worse.

At the moment, there are few studies that demonstrate sildenafil’s ability to actually lower blood pressure. And some studies suggest sildenafil doesn’t help with pulmonary hypertension as much as researchers originally hoped. Despite this, several studies have found that dogs with pulmonary hypertension who take sildenafil have a higher quality of life. 

EXPERT PICKS: WHAT TO READ NEXT

• High blood pressure in dogs: Like people, dogs can have high blood pressure. Learn the symptoms and treatment options for this condition.

• Why dogs vomit: There are many reasons why dogs may vomit. Read about which causes are harmless and which ones may mean it’s time for a visit to your veterinarian.

• Human medicine for pets: Your dog can take some of the same medications as humans, including sildenafil. Here’s how to fill these prescriptions for your pup.

Megaesophagus

Sildenafil was also recently shown to be a promising treatment for canine megaesophagus. Canine megaesophagus is a rare condition that affects the esophagus, the tube that connects the mouth to the stomach. The condition causes the esophagus to widen, which makes it difficult for food to move to the stomach. This causes dogs to regurgitate food, making them more prone to: 

• Aspiration pneumonia

• Weight loss

• Wasting (becoming weak or emaciated)

• Poor quality of life 

Historically, there hasn’t been a medication that helps treat dogs with megaesophagus. But sildenafil seems to help this difficult-to-manage condition.

How is sildenafil (Viagra) given to dogs, and what is the standard dosage?

Sildenafil is available for dogs in 10 mg, 20 mg, 25 mg, and 100 mg tablets. It can also be compounded into a liquid.

The standard dosage of sildenafil for pulmonary hypertension in dogs ranges from 1 mg to 3 mg per kilogram of body weight, given every 8 to 12 hours. The dosage of sildenafil for megaesophagus is 1 mg per kilogram of a dog’s body weight, given every 12 hours.

Sildenafil should be given to dogs on an empty stomach at least 1 hour before feeding or 2 hours after feeding. The medication typically takes effect within 1 to 2 hours.

If your dog has been prescribed sildenafil in a liquid form, shake well before use, if indicated. Measure your dog’s dose carefully, and follow all instructions about giving them the medication and storing it.

Sildenafil is prescribed to dogs off-label. This means that sildenafil is not FDA approved to treat dogs. But many medications are prescribed off-label safely and effectively. 

What are the common side effects of sildenafil (Viagra) in dogs?

Sildenafil is generally safe for most dogs and doesn’t cause many side effects. The most common side effects for dogs include: 

• Skin flushing

• Decreased appetite

• Vomiting

• Diarrhea

If your dog vomits when you give them sildenafil on an empty stomach, give future doses with food. If they still vomit after taking the medication, call your veterinarian for advice. 

Sildenafil is a short-acting medication that stops working within 24 hours for most dogs. But the effects of sildenafil may last longer in dogs with liver disease or kidney disease. 

What are the most serious risks of sildenafil (Viagra) for dogs?

The most serious side effect associated with sildenafil in dogs is low blood pressure. This is rare, but it can happen. So, sildenafil should not be given to dogs that also take medication for high blood pressure, including nitrate medications.

In addition, sildenafil should be used with caution for dogs who have:

• Heart disease

• Low blood pressure

• Dehydration

• Bleeding disorders

Does sildenafil (Viagra) interact with any other dog medications?

Yes, several other medications your dog may take can interact with sildenafil, including:

• Medications for heart disease

• Kidney medications

• High blood pressure medications

• Antifungal medications that end in “-azole,” such as ketoconazole

• Fluoroquinolone antibiotics, such as ciprofloxacin

• Macrolide antibiotics, such as clarithromycin and erythromycin

• Rifampin

• Seizure medications, such as phenobarbital

• Chemotherapy medications, such as paclitaxel

Tell your veterinarian about any medications that your dog takes before starting sildenafil. This includes any vitamins, supplements, or herbs. 

What should you do if your dog misses a dose of sildenafil (Viagra)?

If your dog misses a dose of sildenafil, give them the dose as soon as you remember. Then, wait the normal amount of time between doses before giving them their next dose.

In other words, if you give your dog sildenafil every 12 hours, wait 12 hours from the time you gave them their missed dose until their next one. Never give your dog two doses of the medication at one time. 

What is an alternative to sildenafil for dogs? [nav title="Alternatives"]]

For pulmonary hypertension, there are other medications veterinarians may suggest instead of sildenafil. They include:

• Bosentan

• Sitaxsentan

• Ambrisentan

• Pimobendan

For megaesophagus, dogs do have alternative options to sildenafil. The condition can be treated with the medication pyridostigmine. The steroid prednisone and the medication azathioprine can also be used. But sildenafil may be the best option for megaesophagus.

Why trust our experts?

Written by:

Sarah J. Wooten, DVM, CVJ

Dr. Sarah Wooten, DVM, CVJ, is a well-known international influencer in the veterinary and animal healthcare spaces. She has 16 years of experience in private practice and more than 15 years experience in veterinary media work.

Edited by:

Renée Fabian, MA

Renée Fabian is the senior pet health editor at GoodRx. She’s worked for nearly 10 years as a journalist and editor across a wide range of health and well-being topics.

Reviewed by:

Ghanasyam Bey, DVM

Ghanasyam Bey, DVM, is from Cleveland, Ohio, and attended Princeton University for undergraduate studies. After a year of biology research at Duke University, he attended Ohio State College of Veterinary Medicine.

Our editorial standards

Meet our experts