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, is also used in humans to treat 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 specific disorders in dogs. 

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 decrease the level of calcium inside your dog’s cells, resulting in benefits for certain conditions. 

What is sildenafil (Viagra) used for in dogs?

In dogs, sildenafil is primarily prescribed for two conditions: 

1. Pulmonary hypertension

2. Megaesophagus

Pulmonary hypertension

As mentioned, 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 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. 

Megaesophagus

Sildenafil was also recently shown to be a promising treatment for canine megaesophagus. Canine megaesophagus is a rare condition in dogs 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 has been helpful for 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 in 10 mg, 20 mg, 25 mg, and 100 mg tablets. It can also be compounded into a liquid. An injectable form of sildenafil is available for use in veterinary clinics. 

The standard dosage of sildenafil for pulmonary hypertension in dogs ranges from 0.5 mg to 3 mg per kg of body weight every 8 to 24 hours. The dosage of sildenafil for megaesophagus is 1 mg per kg of a dog’s body weight every 12 hours. 

Sildenafil for dogs should be given on an empty stomach at least 1 hour before feeding or 2 hours after feeding. And 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.  

Use of sildenafil in dogs is considered “off-label” or “extra-label.” This means that sildenafil is not FDA approved for use in dogs. But there are many medications that are prescribed off-label safely and effectively for dogs. 

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

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

• Skin flushing

• Decreased appetite

• Vomiting

• Diarrhea

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

Sildenafil is a short-acting medication that stops working within 24 hours for most dogs. However, the effects of sildenafil may last longer in dogs with liver 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. Therefore, 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 in dogs who have:

• Heart disease

• Low blood pressure

• Dehydration

• Bleeding disorders

Experts don’t know if sildenafil is safe for dogs that are pregnant or nursing. So it may be best to avoid giving the medication to pregnant or nursing dogs. 

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

The following medications are known to have interactions with sildenafil: 

• Medications for heart disease, kidney disease, and high blood pressure

• 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

Be sure to tell your veterinarian about any medications that your dog takes before giving your dog sildenafil. This includes letting your vet know if your dog takes 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 prescribed amount of time between doses after that. 

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

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.

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