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What Is Sildenafil?

Sildenafil is a prescription phosphodiesterase type 5 inhibitor used to treat erectile dysfunction and pulmonary arterial hypertension. It is the active ingredient in Viagra, which is prescribed for erectile dysfunction, and Revatio, which is used for pulmonary arterial hypertension. These products have different approved uses, dosing schedules, and available formulations. Sildenafil relaxes certain blood vessel muscles by increasing signaling through cyclic guanosine monophosphate. In erectile dysfunction, this supports blood flow during sexual stimulation. In pulmonary arterial hypertension, it reduces pulmonary vascular resistance. Sildenafil must not be combined with nitrate medications or the soluble guanylate cyclase stimulator riociguat because dangerous reductions in blood pressure can occur.

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What Is Sildenafil?

Sildenafil is a prescription phosphodiesterase type 5 inhibitor used to treat erectile dysfunction and pulmonary arterial hypertension. It is the active ingredient in Viagra, which is prescribed for erectile dysfunction, and Revatio, which is used for pulmonary arterial hypertension. These products have different approved uses, dosing schedules, and available formulations. Sildenafil relaxes certain blood vessel muscles by increasing signaling through cyclic guanosine monophosphate. In erectile dysfunction, this supports blood flow during sexual stimulation. In pulmonary arterial hypertension, it reduces pulmonary vascular resistance. Sildenafil must not be combined with nitrate medications or the soluble guanylate cyclase stimulator riociguat because dangerous reductions in blood pressure can occur.

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How Does Sildenafil Work?

Sildenafil inhibits phosphodiesterase type 5, an enzyme that breaks down cyclic guanosine monophosphate, or cGMP. This signaling molecule helps relax smooth muscle in blood vessel walls. During sexual stimulation, nitric oxide release increases cGMP activity in penile tissue. By slowing its breakdown, sildenafil supports the blood flow needed for an erection. In pulmonary arterial hypertension, phosphodiesterase type 5 inhibition relaxes blood vessels in the lungs and reduces pulmonary vascular resistance. Sildenafil does not directly cause sexual arousal and does not cure the underlying cause of erectile dysfunction or pulmonary arterial hypertension. Its blood vessel effects also account for important cardiovascular and visual precautions.

What Conditions Does Sildenafil Treat?

Sildenafil is approved for erectile dysfunction in adult men through products such as Viagra. Erectile dysfunction involves difficulty obtaining or maintaining an erection sufficient for sexual activity. Sildenafil is also approved for World Health Organization Group I pulmonary arterial hypertension through products such as Revatio. This condition involves elevated pressure in the arteries supplying the lungs, which can limit physical activity and strain the heart. Revatio is approved for adults and children aged one year and older, with pediatric dosing determined by weight. The formulations and dosing schedules are not interchangeable. A clinician evaluates cardiovascular health, blood pressure, other medications, and treatment eligibility before prescribing sildenafil.

How Should Sildenafil Be Taken?

For erectile dysfunction, sildenafil commonly begins at 50 mg taken as needed approximately one hour before sexual activity. It may be taken 30 minutes to four hours beforehand. The dose can be reduced to 25 mg or increased to 100 mg according to response, with a maximum frequency of once daily. Sildenafil may be taken with or without food, although a high-fat meal can delay its effects. For pulmonary arterial hypertension, Revatio commonly begins at 20 mg orally three times daily in adults, with higher doses used when appropriate. Pediatric treatment is weight-based. Sildenafil must not be combined with nitrates or riociguat. Alpha-blockers and certain other medications may require dose adjustments or additional precautions.

What Are the Side Effects and Warnings of Sildenafil?

Common adverse effects include headache, flushing, nasal congestion, indigestion, dizziness, and temporary visual changes. Serious risks include dangerously low blood pressure, prolonged erections lasting more than four hours, sudden hearing loss, and sudden vision loss associated with nonarteritic anterior ischemic optic neuropathy. Sildenafil must not be taken with nitrate medications or riociguat. Patients with certain heart conditions, low blood pressure, or recent cardiovascular events require careful evaluation. Sildenafil may cause temporary changes in color perception or sensitivity to light. Sudden vision loss, chest pain, fainting, or an erection lasting longer than four hours requires immediate medical attention.

Common Questions About Sildenafil

Is sildenafil the same as Viagra?

Yes. Viagra contains sildenafil and is approved for erectile dysfunction. Revatio also contains sildenafil but is used for pulmonary arterial hypertension.

Can sildenafil treat pulmonary arterial hypertension?

Yes. Sildenafil is approved for pulmonary arterial hypertension through products such as Revatio, using dosing schedules different from those for erectile dysfunction.

Can sildenafil affect eyesight?

Yes. Sildenafil can cause temporary visual disturbances. Sudden vision loss has also been reported and requires immediate medical attention.

Can sildenafil be taken with nitrate medications?

No. Combining sildenafil with nitrates can cause a dangerous drop in blood pressure and is contraindicated.

References

DailyMed - VIAGRA (sildenafil citrate) tablet, film coated. https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=d905dc8d-917f-4ea3-a4ee-a1ecf6967d4e. Date Accessed November 10, 2026.

Sildenafil. LiverTox. https://www.ncbi.nlm.nih.gov/books/NBK548510/. Date Accessed November 10, 2026.

Sildenafil. MedlinePlus. https://medlineplus.gov/druginfo/meds/a699015.html. Date Accessed November 10, 2026.

Sildenafil. PubChem. https://pubchem.ncbi.nlm.nih.gov/compound/Sildenafil. Date Accessed November 10, 2026.

Sildenafil. StatPearls. https://www.ncbi.nlm.nih.gov/books/NBK558978/. Date Accessed November 10, 2026.