Sildenafil
Pronunciation: Not established in the sources reviewed..
- Generic name
- sildenafil
- Brand names
- REVATIO, VIAGRA
- Drug class
- Phosphodiesterase type 5 (PDE5) inhibitor
- Form
- Oral tablets for both products; a solution for intravenous injection is also available for REVATIO. Exact tablet strengths and the IV solution concentration were not extracted from the sources reviewed for this page.
- Route
- Oral (tablets) for pulmonary arterial hypertension and erectile dysfunction; intravenous injection for pulmonary arterial hypertension when oral therapy is temporarily not possible
- Legal status
- US legal/dispensing classification was not specifically extracted from the sources reviewed for this page; this is an evidence gap.
Availability and supply rules vary by country
Trade names by country: United States · Canada
Australia: · Full directory
What sildenafil is and how it works
Sildenafil is a phosphodiesterase type 5 (PDE5) inhibitor. In the United States, it is available under two brand names with different approved uses: REVATIO for pulmonary arterial hypertension (PAH) in adults and children, and VIAGRA for erectile dysfunction (ED) in adult men. Both products share the same active moiety but have different approved uses and dosing. (1) (2)
Sildenafil must only be used for the specific indication for which it has been prescribed. Do not switch between REVATIO and VIAGRA, share your medicine, or change your dose without your prescriber's direction.
Mechanism of action: how sildenafil works
Sildenafil is a phosphodiesterase type 5 (PDE5) inhibitor. A detailed mechanism-of-action statement beyond this classification was not established in the sources reviewed for this page. (1) (2)
What sildenafil is used for
Pulmonary arterial hypertension (PAH)
REVATIO is approved for the treatment of pulmonary arterial hypertension (WHO Group I) in adults and pediatric patients aged 1–17 years, to improve exercise ability and delay clinical worsening. It is taken orally three times a day; an intravenous formulation is available for patients temporarily unable to take oral therapy. (1)
Erectile dysfunction (ED)
VIAGRA is approved for the treatment of erectile dysfunction in adult men. It is taken as needed, approximately 1 hour before sexual activity, with a maximum of one dose per day. (2)
Before taking sildenafil
Do not take / not appropriate for
- Tell your prescriber promptly if you are using, or are prescribed, organic nitrates (such as nitroglycerin) or organic nitrites in any form, regularly or intermittently, before starting or continuing sildenafil — this combination carries a risk of severe hypotension and the prescriber needs to make the safety assessment. (all products) (1) (2)
- Tell your prescriber if you are using riociguat, a guanylate cyclase stimulator, before starting or continuing sildenafil — this combination carries a risk of dangerously low blood pressure and the prescriber needs to make the safety assessment. (REVATIO (this contraindication was extracted from the REVATIO label; a separately verified VIAGRA-label riociguat contraindication was not established in this pass)) (1)
- Tell your prescriber if you have ever had a serious allergic reaction to sildenafil or any component of the product, so they can assess whether sildenafil is appropriate for you. (all products) (1)
Tell your clinician about
- Any heart or blood vessel condition, so they can assess whether sexual activity is medically advisable (for ED) and whether sildenafil is appropriate.
- Any history of low or unstable blood pressure.
- Anatomical deformation of the penis, sickle cell disease, multiple myeloma, leukemia, or any condition that may increase the risk of priapism (prolonged erection).
- Any past sudden vision loss or hearing loss.
- All prescription and over-the-counter medicines you are taking, especially nitrates, riociguat, other PDE5 inhibitors, alpha‑blockers, and CYP3A-affecting medicines, so your prescriber can review the full interaction picture.
- Pregnancy, plans for pregnancy, or breastfeeding (for PAH treatment).
How to take sildenafil
- Sildenafil must be taken exactly as prescribed. The dose, timing, and indication depend on the specific product.
- For pulmonary arterial hypertension (REVATIO): the usual adult dose is 20 mg three times a day. The prescriber may titrate this up to a maximum of 80 mg three times a day based on symptoms and tolerability. Pediatric dosing is weight‑based and determined by the specialist. An intravenous dose (10 mg three times a day as an IV bolus) may be used for patients temporarily unable to take oral therapy.
- For erectile dysfunction (VIAGRA): the recommended starting dose is 50 mg taken as needed, approximately 1 hour before sexual activity; it may be taken from 30 minutes to 4 hours before sexual activity. Based on effectiveness and tolerability, the prescriber may adjust the dose to a maximum of 100 mg or a minimum of 25 mg. Do not take more than one dose per day.
- Do not change your dose, timing, or switch between products without your prescriber's approval.
Procedures and treatment changes
Tell the treating team before surgery, procedures, or any medicine change. Do not alter treatment without the responsible clinician. (1) (2)
Missed dose
A specific missed-dose protocol for REVATIO's three-times-daily regimen was not established in the sources reviewed for this page — contact your prescribing team for advice if you miss a dose. For erectile dysfunction (VIAGRA), the medicine is taken as needed; there is no regular dosing schedule.
Overdose
Specific overdose-management details were not established in the sources reviewed for this page. If you think you have taken too much sildenafil, seek medical attention promptly and let the clinician you see advise on next steps. (1) (2)
Side effects
Sildenafil can cause side effects; not everyone experiences them. The common effects listed below were reported for REVATIO; a separately extracted VIAGRA-specific adverse-reaction list was not reviewed for this page. Serious effects requiring urgent medical attention are listed below.
Headache
What to notice: Mild to moderate headache.
What to do: Tell your treatment team if headaches are severe, persistent, or interfere with daily activities. (1)
Indigestion (dyspepsia) and flushing
What to notice: A feeling of warmth or redness in the face, and stomach discomfort or heartburn.
What to do: These effects are usually temporary; discuss with your prescriber if they are bothersome or worsen. (1)
Muscle aches, back pain, or pain in limbs
What to notice: Aching in muscles, back, or arms/legs.
What to do: Report to your prescriber if severe or lasting. (1)
Diarrhea
What to notice: Loose or frequent bowel movements.
What to do: Mention if persistent or accompanied by other symptoms. (1)
Priapism (prolonged erection)
What to notice: An erection lasting more than 6 hours, with or without pain.
What to do: Seek immediate medical attention; permanent damage can result if not treated promptly. (1)
Sudden vision loss
What to notice: Decreased vision or loss of vision in one or both eyes.
What to do: Seek immediate medical attention. Let the clinician you see advise on whether to continue or stop sildenafil. (1)
Sudden hearing loss
What to notice: A decrease or loss of hearing, sometimes with ringing in the ears or dizziness.
What to do: Seek prompt medical attention. Let the clinician you see advise on whether to continue or stop sildenafil. (1)
Severe low blood pressure (hypotension)
What to notice: Dizziness, fainting, lightheadedness, especially when standing up.
What to do: Seek medical attention promptly. Let the clinician you see advise on whether to continue or stop sildenafil. (1)
Known hypersensitivity to sildenafil
What to notice: Known hypersensitivity to sildenafil or a product component is a contraindication in the source reviewed for this page. A detailed allergic-reaction symptom list was not established in that source.
What to do: Tell your prescriber before starting sildenafil if you have ever had a reaction to it. (1)
Serious warnings
Priapism (prolonged erection) — emergency
Symptoms: An erection that persists more than 6 hours, painful or not.
Action: Go to the nearest emergency department immediately. Permanent injury to the penis can occur. Let the clinician who evaluates you advise on whether to continue or stop sildenafil. (1)
Sudden vision loss (NAION) — emergency
Symptoms: Sudden decrease or loss of vision in one or both eyes.
Action: Seek immediate medical attention. Vision loss can be permanent. Let the clinician who evaluates you advise on whether to continue or stop sildenafil. (1)
Sudden hearing loss — emergency
Symptoms: Sudden decrease or loss of hearing, sometimes accompanied by ringing in the ears or dizziness.
Action: Seek prompt medical evaluation. Let the clinician who evaluates you advise on whether to continue or stop sildenafil. (1)
Known hypersensitivity to sildenafil — warning
Symptoms: Known hypersensitivity to sildenafil or a product component is a contraindication in the source reviewed for this page. A detailed allergic-reaction symptom list was not established in that source.
Action: Tell your prescriber before starting sildenafil if you have ever had a reaction to it, and seek prompt medical attention for any new or unusual symptom after taking it. (1)
Severe hypotension (very low blood pressure) — urgent
Symptoms: Fainting, dizziness, or feeling lightheaded.
Action: Get emergency help. Let the clinician who evaluates you advise on whether to continue or stop sildenafil. (1)
Interactions
| Medicine or test | Effect | Action |
|---|---|---|
| Organic nitrates and nitrites | Sildenafil enhances the blood‑pressure‑lowering effect of nitrates and nitrites, which can cause severe hypotension. | Tell your prescriber about any nitrate or nitrite use, in any form, regularly or intermittently, before starting or continuing sildenafil so they can make the safety decision. (1) (2) |
| Riociguat (REVATIO-label contraindication) | Additive vasodilation can lead to dangerously low blood pressure. This contraindication was extracted from the REVATIO label; a separately verified VIAGRA-label riociguat contraindication was not established in this pass. | Tell your prescriber about any riociguat use before starting or continuing sildenafil so they can make the safety decision. (1) |
| Alpha‑blockers | Both drug classes lower blood pressure, so combined use may add to the blood-pressure-lowering effect. Detailed co-administration guidance beyond this general caution was not established in the sources reviewed for this page. | Tell your prescriber about any alpha-blocker you take so they can factor this into their assessment. (1) |
| Strong CYP3A inhibitors | Concomitant use with REVATIO is not recommended. Specific drug names and the magnitude of effect on sildenafil levels were not established in the sources reviewed for this page. | Tell your prescriber about all medicines you take so they can identify any strong CYP3A inhibitor and decide whether a change is needed. (1) |
| Other PDE5 inhibitors (e.g., VIAGRA and REVATIO together) | Combined safety and effectiveness have not been studied, so this combination should be avoided. | Tell your prescriber if you are using or have been prescribed more than one PDE5 inhibitor so they can review your regimen. (1) |
| CYP3A inducers (e.g., bosentan) | May reduce sildenafil blood levels, potentially decreasing effectiveness. | Your prescriber may adjust the sildenafil dose; do not change it yourself. (1) |
Pregnancy, breastfeeding, kidney/liver function, age
Children and adolescents
Sildenafil for pulmonary arterial hypertension (REVATIO) is approved for pediatric patients aged 1–17 years, with weight‑based dosing. The erectile dysfunction product (VIAGRA) is not indicated for use in children or adolescents. (1)
Pregnancy and breastfeeding
Limited human data on REVATIO use during pregnancy show no clear association with birth defects; animal studies showed no teratogenicity at doses up to 65 times the recommended human dose. Whether REVATIO has any pregnancy-specific use restriction beyond this, and any breastfeeding-specific data, were not established in the sources reviewed for this page — discuss with your prescriber. VIAGRA is approved for erectile dysfunction in adult men; separate data on use in women were not reviewed for this page. (1)
Men at risk of priapism
Men with anatomical penile conditions (such as angulation, cavernosal fibrosis, or Peyronie's disease) or conditions that may predispose to priapism (sickle cell anemia, multiple myeloma, leukemia) should use sildenafil with caution and immediately seek help if an erection lasts more than 6 hours. (1)
Monitoring
Before starting
- Confirm the exact indication and the appropriate product for that indication (PAH vs. ED) with the prescriber.
- Tell the prescriber about cardiovascular history, risk factors for priapism, and any history of vision or hearing loss, so they can assess suitability — a specific required work-up protocol was not established in the sources reviewed for this page.
- List all current medicines, especially nitrates, riociguat, alpha‑blockers, antihypertensives, CYP3A-affecting medicines, and other PDE5 inhibitors.
During treatment
- Watch for signs of hypotension, priapism, changes in vision, and hearing loss, and seek prompt medical attention if any occur.
- A specific PAH reassessment schedule or pediatric growth-related dose-evaluation protocol was not established in the sources reviewed for this page; follow the treating team's guidance.
- Tell the prescriber about any alpha-blocker, nitrate, riociguat, or other PDE5 inhibitor use so they can review the full medication regimen.
Storage
Specific storage instructions for sildenafil were not established in the sources reviewed for this page. Follow the storage instructions on the prescription label.
Professional information
Clinician‑facing context only. Refer to the full local prescribing information and current guidelines for each indication.
United States
Indication: Pulmonary arterial hypertension (REVATIO)
Dose summary: Adults: 20 mg orally three times daily; may titrate to maximum 80 mg three times daily based on symptoms and tolerability. Intravenous: 10 mg bolus three times daily for patients temporarily unable to take oral therapy. Pediatric (age 1–17): ≤20 kg — 10 mg three times daily; >20 kg — 20 mg three times daily (may increase to 40 mg three times daily for >45 kg).
Renal context: Specific dose‑adjustment data for renal impairment not established in the reviewed labeling; refer to full prescribing information. (1)
United States
Indication: Erectile dysfunction (VIAGRA)
Dose summary: Most patients: 50 mg taken as needed approximately 1 hour before sexual activity, with a window of 30 minutes to 4 hours. Dose may be adjusted to 25 mg or 100 mg based on effectiveness and tolerability. Maximum dosing frequency: once per day.
Renal context: Specific dose‑adjustment data for renal impairment not established in the reviewed labeling; refer to full prescribing information. (2)
Hepatic guidance
Dose adjustment in hepatic impairment has not been specifically addressed in the sources reviewed for this page; this is an evidence gap.
Overdose note
Specific overdose-management protocol details, including whether a specific antidote exists, were not established in the sources reviewed for this page; this is an evidence gap. (1) (2)
Frequently asked questions
Can I take sildenafil with nitroglycerin or other organic nitrates or nitrites?
This combination is a contraindication in the sources reviewed for this page because it can cause a dangerous drop in blood pressure. Let your prescriber make the safety decision about any nitrate or nitrite you use. (1) (2)
Can I take REVATIO and VIAGRA together?
These two products contain the same active ingredient but are for different conditions. Combining REVATIO with VIAGRA or any other PDE5 inhibitor should be avoided because their combined safety and effectiveness have not been studied. Tell your prescriber if you are using or have been prescribed more than one PDE5 inhibitor so they can review your regimen. (1)
What should I do if I have an erection that lasts more than 6 hours?
Seek emergency medical attention immediately. An erection lasting that long can permanently damage the penis if not treated promptly. (1)
Can I take sildenafil every day?
For pulmonary arterial hypertension (REVATIO), it is prescribed three times daily. For erectile dysfunction (VIAGRA), it is taken only as needed, no more than once per day. Follow your prescription exactly. (1) (2)
What is the mechanism of action of sildenafil?
Sildenafil is a phosphodiesterase type 5 (PDE5) inhibitor. A detailed mechanism-of-action statement beyond this classification was not established in the sources reviewed for this page. (1) (2)
References
- REVATIO (sildenafil) prescribing informationU.S. Food and Drug Administration · United States · dated 2026 · accessed 2026-08-05 · source 1
- VIAGRA (sildenafil citrate) prescribing informationU.S. Food and Drug Administration · United States · dated 2026 · accessed 2026-08-05 · source 2
- SILDENAFIL TABLET [BRYANT RANCH PREPACK] — US prescribing information (DailyMed SPL)U.S. National Library of Medicine (DailyMed) · US · accessed 2026-08-14 · source 3
- Sildenafil — patient drug information (MedlinePlus)U.S. National Library of Medicine (MedlinePlus) · US · accessed 2026-08-14 · source 4
- SILDENAFIL CITRATE — FDA approval record (Drugs@FDA ANDA209302)U.S. Food and Drug Administration · US · accessed 2026-08-14 · source 5
- sildenafil — RxNorm normalized drug concept (RXCUI 136411)U.S. National Library of Medicine (RxNorm) · US · accessed 2026-08-14 · source 6
Brand names by country
Single-ingredient sildenafil names are shown separately by country. Product availability, strengths, and supply rules can change; combination products are not included here.
Priority countries
United States
- Viagra100 mg, 25 mg, 50 mg · pfizer laboratories div pfizer inc
- Revatio20 mg, 10 mg/mL, .8 mg/mL · pfizer laboratories div pfizer inc
- Vybrique100 mg, 25 mg, 50 mg, 75 mg · ibsa pharma inc.
Canada
- VIAGRA
- MYL-SILDENAFIL
- REVATIO
- RATIO-SILDENAFIL R
- PMS-SILDENAFIL R
- APO-SILDENAFIL R