sildenafil
Brand names: Viagra, Revatio
Sildenafil is a medicine used to treat erectile dysfunction (ED) in men. It helps increase blood flow to the penis to get and keep an erection.
Drug Pricing (NADAC)
Brand Price
$83.94/unit
Generic Price
$0.62/unit
Generic Savings
99%
Generic Available
Yes (36 manufacturers)
Pricing data from NADAC (CMS), effective December 18, 2024. Compare all drug costs →
What it does
Sildenafil is used to treat erectile dysfunction (ED), also known as impotence, in men.
Common side effects
Headache, Flushing (redness of the skin), Upset stomach
Key warnings
You should not take sildenafil if you are taking nitrates for chest pain, as this can cause a dangerous drop in blood pressure.
How It Works
Sildenafil belongs to a class of drugs called PDE5 inhibitors. It works by relaxing the muscles and increasing blood flow to the penis during sexual stimulation. This helps you get and keep an erection.
How to Take It
Take sildenafil about 1 hour before sexual activity, but you can take it between 30 minutes and 4 hours before. The usual starting dose is 50 mg. Your doctor may change your dose to 25 mg or 100 mg based on how well it works and how your body reacts. Do not take more than one dose of sildenafil per day. You can take sildenafil with or without food.
Pregnancy & Breastfeeding
Sildenafil is not for use in women. It is not known if sildenafil can harm an unborn baby or pass into breast milk.
Missed Dose
Since sildenafil is taken as needed, you are not likely to miss a dose. If you do, just take it as soon as you remember, but do not take more than one dose per day.
Storage
Store sildenafil tablets at room temperature, away from heat and moisture.
Side Effects (from patient reports)
Based on 41,358 FDA adverse event reports.
FDA Adverse Event Report Analysis
Detailed analysis of 55,325 reports from the FDA Adverse Event Reporting System (FAERS). Reports span 2004–2025.
Total Reports
55,325
Death-Related Reports
8,392
Hospitalization Reports
24,609
Top Indication
Pulmonary Arterial Hypertension
Gender Distribution
Age Distribution
Most Reported Adverse Reactions (FAERS)
| # | Reaction | Reports |
|---|---|---|
| 1 | DYSPNOEA | 7,729 |
| 2 | HEADACHE | 5,655 |
| 3 | DIARRHOEA | 4,447 |
| 4 | NAUSEA | 3,984 |
| 5 | DEATH | 3,873 |
| 6 | FATIGUE | 3,799 |
| 7 | DIZZINESS | 3,256 |
| 8 | DRUG INEFFECTIVE | 3,068 |
| 9 | COUGH | 2,921 |
| 10 | PNEUMONIA | 2,628 |
| 11 | VOMITING | 2,394 |
| 12 | HYPOTENSION | 2,360 |
| 13 | OFF LABEL USE | 2,259 |
| 14 | MALAISE | 2,168 |
| 15 | PAIN | 2,011 |
Reactions in Death Reports
Reactions in Hospitalization Reports
Source: FDA FAERS (Adverse Event Reporting System) FDA FAERS (Adverse Event Reporting System) Reports are voluntary and do not establish causation
Serious Warnings
You should not take sildenafil if you are taking nitrates for chest pain, as this can cause a dangerous drop in blood pressure. If you have an erection that lasts longer than 4 hours, get medical help right away. Stop taking sildenafil and seek medical attention if you have a sudden loss of vision or hearing.
Known Drug Interactions
7 DRUG INTERACTIONS Sildenafil can potentiate the hypotensive effects of nitrates, alpha blockers, and anti-hypertensives ( 4.1 , 5.5 , 7.1 , 7.2 , 7.3 , 12.2 ) With concomitant use of alpha blockers, initiate sildenafil at 25 mg dose ( 2.3 ) CYP3A4 inhibitors (e.g., ritonavir, ketoconazole, itraconazole, erythromycin): Increase sildenafil exposure ( 2.4 , 7.4 , 12.3 ) Ritonavir: Do not exceed a maximum single dose of 25 mg in a 48 hour period ( 2.4 , 5.6 ) Erythromycin or strong CYP3A4 inhibitors (e.g., ketoconazole, itraconazole, saquinavir): Consider a starting dose of 25 mg ( 2.4 , 7.4 ...
Mechanism: Ketoconazole slows down the breakdown of sildenafil, which can lead to higher levels of the drug in your system.
What to do: Your doctor should consider starting you on a lower dose of 25 mg of sildenafil.
7 DRUG INTERACTIONS Sildenafil can potentiate the hypotensive effects of nitrates, alpha blockers, and anti-hypertensives ( 4.1 , 5.5 , 7.1 , 7.2 , 7.3 , 12.2 ) With concomitant use of alpha blockers, initiate sildenafil at 25 mg dose ( 2.3 ) CYP3A4 inhibitors (e.g., ritonavir, ketoconazole, itraconazole, erythromycin): Increase sildenafil exposure ( 2.4 , 7.4 , 12.3 ) Ritonavir: Do not exceed a maximum single dose of 25 mg in a 48 hour period ( 2.4 , 5.6 ) Erythromycin or strong CYP3A4 inhibitors (e.g., ketoconazole, itraconazole, saquinavir): Consider a starting dose of 25 mg ( 2.4 , 7.4 ...
Mechanism: Erythromycin prevents your body from processing sildenafil normally, which increases the amount of medicine in your blood.
What to do: Your doctor should consider starting you on a lower dose of 25 mg of sildenafil.
7 DRUG INTERACTIONS Sildenafil can potentiate the hypotensive effects of nitrates, alpha blockers, and anti-hypertensives ( 4.1 , 5.5 , 7.1 , 7.2 , 7.3 , 12.2 ) With concomitant use of alpha blockers, initiate sildenafil at 25 mg dose ( 2.3 ) CYP3A4 inhibitors (e.g., ritonavir, ketoconazole, itraconazole, erythromycin): Increase sildenafil exposure ( 2.4 , 7.4 , 12.3 ) Ritonavir: Do not exceed a maximum single dose of 25 mg in a 48 hour period ( 2.4 , 5.6 ) Erythromycin or strong CYP3A4 inhibitors (e.g., ketoconazole, itraconazole, saquinavir): Consider a starting dose of 25 mg ( 2.4 , 7.4 ...
Mechanism: Itraconazole stops the body from breaking down sildenafil, which can cause the drug to build up to higher levels.
What to do: Your doctor should consider starting you on a lower dose of 25 mg of sildenafil.
avanafil, sildenafil, tadalafil, vardenafil ↑ PDE-5 inhibitors (only the use of sildenafil at doses used for treatment of erectile dysfunction has been studied with darunavir/ritonavir) Co-administration with darunavir/ritonavir may result in an increase in PDE-5 inhibitor-associated adverse events, including hypotension, syncope, visual disturbances and priapism. Use of PDE-5 inhibitors for pulmonary arterial hypertension (PAH): Co-administration with sildenafil used for PAH is contraindicated due to potential for sildenafil associated adverse reactions (which include visual disturbances, ...
Mechanism: Darunavir increases the amount of sildenafil in your system, which can cause very low blood pressure or fainting.
What to do: Avoid using these drugs together, as the combination can lead to dangerous side effects like vision changes or fainting.
7 DRUG INTERACTIONS 7.1 Phosphodiesterase Inhibitors BiDil is contraindicated in patients who are using a selective inhibitor of cyclic guanosine monophosphate (cGMP)-specific phosphodiesterase type 5 (PDE5), PDE5 inhibitors such as avanafil, sildenafil, vardenafil, and tadalafil have been shown to potentiate the hypotensive effects of organic nitrates.
Mechanism: Both drugs work to relax blood vessels, and taking them together can cause your blood pressure to drop to a dangerously low level.
What to do: Do not take these two medications together.
Common Questions
How long does sildenafil last?
Can I take sildenafil every day?
What should I avoid while taking sildenafil?
Can I drink alcohol while taking sildenafil?
What if sildenafil doesn't work for me?
Is sildenafil safe for everyone?
Can sildenafil affect my heart?
Does sildenafil increase my sex drive?
Can I buy sildenafil over the counter?
What should I tell my doctor before taking sildenafil?
What are the common side effects of sildenafil?
Does sildenafil interact with other medications?
What drug class is sildenafil?
Is there a generic version of sildenafil?
Is sildenafil safe during pregnancy?
Related Medications in PDE5 Inhibitor
Other drugs grouped near sildenafil — same-class peers and common alternatives.
alfuzosin
Uroxatral
Alfuzosin is a medicine that helps men with enlarged prostate glands.
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bethanechol
Urecholine
Bethanechol helps you to urinate if you have trouble emptying your bladder.
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darifenacin
Enablex
Darifenacin (Enablex) is a medicine that helps control an overactive bladder.
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dutasteride
Avodart
Dutasteride and tamsulosin hydrochloride capsules contain two medicines to treat enlarged prostate in men.
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dutasteride/tamsulosin
Jalyn
This medicine combines two drugs to treat enlarged prostate in men.
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Medication Guides
Understanding Drug Interactions
How CYP450 enzymes, inhibitors, and inducers affect your medications
Generic vs Brand Name Drugs
FDA requirements, cost savings, and when the difference matters
Narrow Therapeutic Index Drugs
Why some drugs demand precise dosing and monitoring
Common Drug Interactions
Dangerous medication combinations and how to protect yourself
Related Health & Safety Data
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What the FDA Data Shows for sildenafil
The FDA label for sildenafil (sold under brand names such as Viagra, Revatio) classifies it as a prescription-only medication in the PDE5 Inhibitor class. Sildenafil is used to treat erectile dysfunction (ED), also known as impotence, in men. Official labeling lists 10 commonly reported side effects, including Headache, Flushing (redness of the skin), Upset stomach.
Post-market surveillance from the FDA Adverse Event Reporting System (FAERS) captures real-world experience. For this drug, FAERS contains 41,358 voluntary reports. The database also lists 10 documented drug interactions derived from FDA labeling, with the top-flagged interaction rated major severity. NADAC pricing from CMS shows a generic unit cost of $0.62 versus $83.94 for the brand — a 99% generic savings.
Report counts do not establish causation — a FAERS entry documents a temporal association, not proof that the drug produced the outcome. Widely prescribed medications naturally accumulate more reports than niche therapies, so raw totals must be interpreted alongside total exposure. Shortage status, recall history, and patent information further shape supply and switching decisions. This page summarizes public FDA data for educational purposes only and is not a substitute for professional medical advice — always consult a licensed healthcare provider before starting, stopping, or changing any medication.
Data Sources
Drug labeling: FDA Drug Labels (SPL/DailyMed). Adverse events: FDA Adverse Event Reporting System (FAERS). Pricing: CMS National Average Drug Acquisition Cost (NADAC).
FAERS reports are voluntary and do not establish causation. Drug interactions are derived from FDA labeling and clinical references. Always consult a healthcare professional before making medication decisions.
Last updated: April 4, 2025
Read our methodology — how this data is sourced, computed, and verified.
All federal data sources used on this page
- FDA Orange Book — approved drug products with therapeutic equivalence. accessdata.fda.gov/cder/ob
- FDA DailyMed — NIH-hosted drug labeling for FDA-approved meds. dailymed.nlm.nih.gov
- FDA Adverse Event Reporting System (FAERS) — post-marketing safety surveillance. fda.gov/drugs/faers
- NLM RxNorm — standardized clinical drug nomenclature. nlm.nih.gov/research/umls/rxnorm
- CMS Medicare Part B Drug Average Sales Price Files — federal drug pricing data. cms.gov/medicare/part-b-drugs/asp
- FDA Drug Shortages Database — current and resolved drug shortage tracking. accessdata.fda.gov/drugshortages