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Generic Name: Sildenafil, Sildenafil citrate

Brands: Viagra, Revatio

Class: Phosphodiesterase-5 (PDE5) inhibitors

Availability: Prescription only

Molecular Formula: C28H38N6O11S

Substance UNII: BW9B0ZE037

What is Sildenafil?

Sildenafil is a phosphodiesterase-5 (PDE5) inhibitor. It is often sold under the brand names Viagra and Revatio. Sildenafil is also an ingredient found in another medication sold in some countries under the brand name Caverta. 

What is Sildenafil Used For?

According to MedlinePlus.gov, sildenafil (as Viagra) is used to treat erectile dysfunction (impotence). It does this by increasing blood flow to the penis and promoting an erection.

Sildenafil (as Revatio) is also used to treat pulmonary arterial hypertension (PAH) in some adults. PAH happens when there is high blood pressure inside the arteries that bring blood to the lungs. This behavior reduces blood flow to the lungs and can lead to shortness of breath, fatigue, dizziness. PAH can also make it harder to perform physical activities, because the heart has to work harder to pump blood into the lungs. By relaxing the blood vessels in the lungs, sildenafil therefore helps manage PAH, prevents the condition from worsening, and makes it easier for people with this condition to exercise.

Off-label uses for sildenafil include treatment for Raynaud’s phenomenon, high altitude pulmonary edema (swelling and excess fluid in the lungs), and a condition known as female sexual arousal disorder (FSAD).

How Does Sildenafil Work?

As a PDE5 inhibitor, sildenafil helps improve blood flow by relaxing blood vessels and helping them widen (vasodilate). 

PDE5 is an enzyme in the body that acts on the cardiovascular system. One of PDE5’s roles is to break down another substance called cyclic guanosine monophosphate (GMP). Cyclic GMP normally causes blood vessels to relax and widen (vasodilate). Since PDE5 breaks down cyclic GMP, it effectively prevents blood vessels from dilating. That’s why a drug like sildenafil, which blocks or inhibits the activity of PDE5, promotes vasodilation, because it helps prevent cyclic GMP from being broken down and allows it to do its job of relaxing and widening the blood vessels and arteries. In other words, sildenafil works by blocking the enzyme that normally blocks vasodilation.

Sildenafil is usually taken orally in pill form, although it is available in liquid form (as Revatio) or even as an intravenous (IV) injection in some instances. Revatio contains a lower dose of sildenafil and is usually taken about three times per day. Viagra contains a higher dose of sildenafil and is taken no more than once per day.

How Long Does it Take for Sildenafil to Work?

Sildenafil typically starts working within 30 to 60 minutes after taking it, but it may take up to 2 hours. For example, improvements in blood pressure for people with PAH can be seen within 1 to 2 hours after taking sildenafil (as Revatio). If the medication is taken to treat erectile dysfunction, it’s important to remember that a person still needs to feel sexually aroused in order to get an erection, even after taking sildenafil. That is to say, the medication won’t create an erection “on its own.” 

The effects of sildenafil typically last for about 4 hours. Research shows that the drug is generally well-tolerated.

Do Not Use Sildenafil If:

There are several situations where this medication may not be the right choice for you. According to the U.S. National Library of Medicine, individuals should not take sildenafil in the following situations and/or if they have the following conditions: 

  • Use of certain medications, including nitrates (nitroglycerin sublingual (Nitrostat), isosorbide mononitrate) , nitric oxide donors, alpha blockers, and guanylate cyclase stimulators 
  • An allergy to sildenafil (unlikely, but possible)
  • Poorly controlled high blood pressure (hypertension)

Please note that this list may not be complete, and there may be other situations where sildenafil use is not advisable.

Disclaimer: this article does not constitute or replace medical advice. If you have an emergency or a serious medical question, please contact a medical professional or call 911 immediately. To see our full medical disclaimer, visit our Terms of Use page.


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