What Is Silenafil and How Does It Work?

Sildenafil is used to treat male sexual function problems (impotence or erectile dysfunction-ED). In combination with sexual stimulation, sildenafil works by increasing blood flow to the penis to help a man get and keep an erection.

Sildenafil does not protect against sexually transmitted diseases (such as HIV, hepatitis B, gonorrhea, syphilis). Practice "safe sex" such as using latex condoms. Consult your doctor or pharmacist for more details.

Sildenafil is also available in other brands and strengths for treating high blood pressure in the lungs (pulmonary hypertension). Do not take sildenafil with any other product that contains sildenafil or other similar medications for erectile dysfunction-ED or pulmonary hypertension (such as tadalafil, vardenafil).

Sildenafil is available under the following different brand names: Revatio, and Viagra.

Dosages of Sildenafil

Dosage Forms and Strengths

Tablet (Revatio)

  • 20 mg

Tablet (Viagra)

  • 25 mg
  • 50 mg
  • 100 mg

Injectable solution (Revatio)

  • 10 mg/12.5mL

Oral suspension (Revatio)

  • 10 mg/12.5mL (when reconstituted)

Dosage Considerations – Should be Given as Follows:

Erectile Dysfunction


  • 50 mg orally 1 hour before sexual activity
  • may be increased to 100 mg or reduced to 25 mg, depending on effectiveness and tolerance
  • not to exceed 100 mg/day

Pulmonary Arterial Hypertension


  • Oral: 5 mg or 20 mg 3 times daily, administered 4-6 hours apart
  • Intravenous (IV): 2.5-mg or 10-mg bolus 3 times daily if patient is temporarily unable to take orally
  • Recommended oral/IV dose not to be exceeded
  • Adding Revatio to bosentan does not have any beneficial effect on exercise capacity

Dosing Modifications

  • Hepatic impairment or severe renal impairment: Use initial dose of 25 mg

Geriatric Dosing

Erectile Dysfunction

  • Viagra
  • Older than 65 years: 25 mg orally initially 1 hour before sexual activity

Pulmonary Arterial Hypertension

  • Revatio
  • Oral: 5 mg or 20 mg 3 times daily, administered 4-6 hours apart
  • Intravenous (IV): 2.5-mg or 10-mg bolus 3 times daily if patient is temporarily unable to take orally
  • Recommended oral/IV dose not to be exceeded
  • Adding Revatio to bosentan does not have any beneficial effect on exercise capacity
  • Clinical trials found no significant difference in response between elderly patients and younger adults; however, cautious dose selection should be considered in elderly because of greater frequency of decreased hepatic, renal, and cardiac function, as well as comorbid conditions and concomitant pharmacotherapy
  • Compared with healthy younger volunteers, healthy elderly volunteers (65 years and older) had reduced clearance of sildenafil, resulting in approximately 84% and 107% higher plasma concentrations of sildenafil and its active N-desmethyl metabolite, respectively


  • Not to be prescribed to children (1-17 years) for pulmonary arterial hypertension (PAH); this recommendation against use is based on long-term clinical pediatric trial showing that children taking high doses had higher risk of death than children taking low doses and that low doses were not effective in improving exercise ability

What Are Side Effects Associated with Using Sildenafil?

Side effects associated with use of Sildenafil, include the following:

  • Headache
  • Flushing
  • Nosebleed
  • Indigestion
  • Insomnia
  • Skin redness
  • Diarrhea
  • Dizziness
  • Skin rash

Postmarketing side effects of sildenafil reported include:

  • Vaso-occlusive crisis (PAH secondary to sickle-cell anemia)

This document does not contain all possible side effects and others may occur. Check with your physician for additional information about side effects.

What Other Drugs Interact with Sildenafil?

If your medical doctor is using this medicine to treat your pain, your doctor or pharmacist may already be aware of any possible drug interactions and may be monitoring you for them. Do not start, stop, or change the dosage of any medicine before checking with your doctor, health care provider or pharmacist first.

Severe Interactions of sildenafil include:

Sildenafil has serious interactions with at least 48 different drugs.

Sildenafil has moderate interactions with at least 72 different drugs.

Mild Interactions of sildenafil include:

This information does not contain all possible interactions or adverse effects. Therefore, before using this product, tell your doctor or pharmacist of all the products you use. Keep a list of all your medications with you, and share this information with your doctor and pharmacist. Check with your health care professional or doctor for additional medical advice, or if you have health questions, concerns or for more information about this medicine.

What Are Warnings and Precautions for Sildenafil?


  • This medication contains sildenafil
  • Do not take Revatio or Viagra if you are allergic to sildenafil or any ingredients contained in this drug.
  • Keep out of reach of children. In case of overdose, get medical help or contact a Poison Control Center immediately


  • Hypersensitivity
  • Soluble guanylate cyclase (sGC) stimulators (e.g., riociguat); concomitant use can cause hypotension
  • Co-administration with nitrates:
    • Co-administration with nitrates (either regularly and/or intermittently) and nitric oxide donors
    • Consistent with the effects of PDE5 inhibition on the nitric oxide/cyclic guanosine monophosphate pathway, PDE5 inhibitors may potentiate the hypotensive effects of nitrates
    • A suitable time interval following PDE5 dosing for the safe administration of nitrates or nitric oxide donors has not been determined

Effects of Drug Abuse

No information provided

Short-Term Effects

  • Elicits vasodilatory properties, resulting in mild and transient decreases in blood pressure.
  • See "What Are Side Effects Associated with Using Sildenafil?"

Long-Term Effects

  • Prolonged use may result in overgrowth of nonsusceptible organisms, including fungi
  • See "What Are Side Effects Associated with Using Sildenafil?”


  • Elicits vasodilatory properties, resulting in mild and transient decreases in blood pressure
  • Use with caution in patients with anatomic deformation of penis (e.g., angulation, cavernosal fibrosis, or Peyronie disease), conditions potentially predisposing to priapism (e.g., sickle cell anemia, multiple myeloma, or leukemia), cardiovascular disease, bleeding disorders, active peptic ulcer disease, liver disease, renal impairment, multidrug antihypertensive regimens, retinitis pigmentosa, concomitant use of CYP3A4 inhibitors
  • Pulmonary vasodilators may significantly worsen cardiovascular status of patients with pulmonary veno-occlusive disease
  • Patients taking alpha blocker should be stabilized before starting phosphodiesterase (PDE)-5 inhibitor, which should be initiated at lowest dose; if patient is already taking optimized dose of PDE-5 inhibitor, alpha blocker should be initiated at lowest dose to avoid hypotension
  • Not to be taken with other PDE-5 inhibitors
  • Sudden decrease or loss of hearing, which may be accompanied by tinnitus and dizziness
  • Viagra: Patients should stop sildenafil and seek medical care if a sudden loss of vision occurs in 1 or both eyes, which could be a sign of non-arteritic anterior ischemic optic neuropathy (NAION); use with caution, and only when the anticipated benefits outweigh the risks, in patients with a history of NAION; patients with a ”crowded” optic disc may also be at an increased risk of NAION
  • Viagra: Potential for cardiac risk with sexual activity in patients with preexisting cardiovascular disease; therefore, treatment for erectile dysfunction generally should not be instituted in men for whom sexual activity is inadvisable because of their underlying cardiovascular status
  • May cause dose-related impairment of color discrimination; use caution in patients with retinitis pigmentosa
  • Evaluate underlying causes of erectile dysfunction or BPH before initiating therapy
  • Revatio: In small, prematurely terminated study of patients with PAH secondary to sickle-cell disease, vaso-occlusive crises requiring hospitalization were more commonly reported by patients who received sildenafil than by those randomized to placebo; effectiveness of sildenafil in PAH secondary to sickle-cell anemia has not been established; the clinical relevance to men treated for erectile dysfunction with sildenafil is not known
  • Revatio: Not for use in children with PAH; increased mortality with increasing doses (hazard ratio 3.5) was observed in randomized, double-blind, placebo-controlled clinical trial of 234 children (1-17 years) with PAH who had mild-to-moderate symptoms at baseline
  • Revatio: Epistaxis occurred in 13% of patients with PAH secondary to connective tissue disease (e.g., scleroderma); this effect was not seen in idiopathic PAH; incidence was also higher in those receiving concomitant PO vitamin K antagonist therapy (9%) than in those not receiving such therapy (2%)

Pregnancy and Lactation

  • Sildenafil may be acceptable for use during pregnancy
  • Either animal studies show no risk but human studies are not available, or animal studies showed minor risks and human studies were done and showed no risk
  • It is unknown whether sildenafil is distributed into breast milk. Consult your doctor before breastfeeding
Medscape. Sildenafil.

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