Sildenafil (Viagra) is used to treat erectile dysfunction (impotence or an inability to get or keep an erection) in men.¹ Sildenafil can also be used to treat premature ejaculation.^2,3

Sildenafil is in a class of medications called phosphodiesterase (PDE) inhibitors and treats erectile dysfunction by increasing blood flow to the penis during sexual stimulation.⁴ It may also be effective for treating premature ejaculation, particularly when paired with an SSRI such as citalopram (Celexa®), escitalopram (Lexapro®) and Sertraline (Zoloft®).^5,6

Sildenafil usually begins to work for erectile dysfunction within 30 minutes.⁷

The effects of sildenafil typically last up to four hours, with the effectiveness starting to wear off after two hours. If you experience a prolonged or painful erection for four hours or more, contact your doctor immediately.⁸

Sildenafil can take five or six hours to fully leave your system, but a high dosage may take longer.⁹

Do not take sildenafil more than once per day. Always follow medication instructions exactly as prescribed.¹⁰

Your healthcare provider will tell you how much to take and when to take it based on your physical health, your symptoms and other factors. Do not exceed their recommended dosage.¹¹

If you are taking sildenafil to treat erectile dysfunction, follow your doctor's directions. Take sildenafil as needed before sexual activity. The best time to take sildenafil is about one hour before sexual activity, but you can take the medication any time from four hours to 30 minutes before sexual activity. Sildenafil usually should not be taken more than once every 24 hours. If you have certain health conditions or are taking certain medications, your doctor may tell you to take sildenafil less often. You can take sildenafil with or without food. However, if you take sildenafil with a high-fat meal, it will take longer for the medication to start to work.

Follow the directions on your prescription label carefully and ask your doctor or pharmacist to explain any part you do not understand. Take sildenafil exactly as directed. Do not take more or less of it, or take it more often than prescribed by your doctor.

If you are taking sildenafil for erectile dysfunction, your doctor will probably start you on 50 mg of sildenafil and increase or decrease your dose depending on your response to the medication. Tell your doctor if sildenafil is not working well or if you are experiencing side effects.¹²

Sildenafil tablets for erectile dysfunction come in different strengths ranging from 20 mg to 100 mg. The usual dose is 50 mg, taken once per day when you need it. The dose can be increased to 100 mg or decreased to 25 mg depending on its effect.¹³

Sildenafil is prescribed off-label for premature ejaculation but has been found effective in 50 mg dosages.¹⁴ Work with your healthcare provider to find the right dosage for you.

Without insurance, sildenafil can cost as much as $15 per tablet.¹⁵ RedBox Rx offers sildenafil for as low as $1 per tablet.

Sildenafil requires a doctor’s prescription and is not available over the counter.¹⁶ Start an online consult for erectile dysfunction or premature ejaculation with RedBox Rx to find fast, affordable and discreet support.

Sildenafil is not FDA-approved for women but may be prescribed in certain situations.¹⁷

PDE5 inhibitors such as sildenafil, tadalafil, avanafil and vardenafil all work in the same basic way by relaxing blood vessels to increase blood flow to the penis. They are all effective for treating erectile dysfunction, but they differ mainly in how quickly they start working and how long their effects last.¹⁸

Read our Complete Guide to Compare ED Medications to learn more.

Yes, sildenafil does expire. It typically has a shelf life of about two years, but check your medication’s bottle for a more specific date.¹⁹

Before taking sildenafil:

• Tell your doctor and pharmacist if you are allergic to sildenafil, any other medications or any of the ingredients in sildenafil products. Ask your pharmacist for a list of the ingredients.

• Do not take sildenafil if you are taking or have recently taken riociguat (Adempas) or nitrates (medications for chest pain) such as isosorbide dinitrate (Isordil), isosorbide mononitrate (Monoket) and nitroglycerin (Minitran, Nitro-Dur, Nitromist, Nitrostat, others). Nitrates come as tablets, sublingual (under the tongue) tablets, sprays, patches, pastes and ointments. Ask your doctor if you are not sure whether any of your medications contain nitrates.

• Do not take street drugs containing nitrates such as amyl nitrate and butyl nitrate (“poppers”) while taking sildenafil.

• Tell your doctor and pharmacist what prescription and nonprescription medications, vitamins and nutritional supplements you are taking or plan to take. Be sure to mention any of the following: alpha blockers such as alfuzosin (Uroxatral), doxazosin (Cardura), prazosin (Minipress), tamsulosin (Flomax, in Jalyn) and terazosin; amlodipine (Norvasc, in Amturnide, in Tekamlo); certain antifungals such as itraconazole (Onmel, Sporanox) and ketoconazole (Nizoral); anticoagulants (“blood thinners”) such as warfarin (Coumadin, Jantoven); certain barbiturates such as butalbital (in Butapap, in Fioricet, others) and secobarbital (Seconal); beta blockers such as atenolol (Tenormin, in Tenoretic), labetalol (Trandate), metoprolol (Lopressor, Toprol-XL, in Dutoprol), nadolol (Corgard, in Corzide) and propranolol (Hemangeol, Inderal LA, InnoPran); bosentan (Tracleer); cimetidine; efavirenz (Sustiva, in Atripla); erythromycin (E.E.S., E-Mycin, Erythrocin); HIV protease inhibitors including amprenavir (Agenerase; no longer available in the U.S.), atazanavir (Reyataz, in Evotaz), darunavir (Prezista, in Prezcobix), fosamprenavir (Lexiva), indinavir (Crixivan), lopinavir (in Kaletra), nelfinavir (Viracept), ritonavir (Norvir, in Kaletra), saquinavir (Invirase) and tipranavir (Aptivus); nevirapine (Viramune); other medications or devices to treat erectile dysfunction; medications for high blood pressure; certain medications for seizures, including carbamazepine (Carbatrol, Epitol, Tegretol, others), phenobarbital and phenytoin (Dilantin, Phenytek); rifabutin (Mycobutin); and rifampin (Rifadin, Rimactane, in Rifamate, in Rifater). Your doctor may need to change the doses of your medications or monitor you carefully for side effects. Many other medications may also interact with sildenafil, so be sure to tell your doctor about all the medications you are taking, even those that do not appear on this list.

• Tell your doctor what herbal products you are taking or plan to take, especially St. John's wort.

• Tell your doctor if you smoke, if you have ever had an erection that lasted for several hours and if you have recently lost a large amount of body fluids (dehydration). This can happen if you are sick with fever, diarrhea or vomiting; sweat a lot; or do not drink enough liquids. Also tell your doctor if you have or have ever had pulmonary veno-occlusive disease (PVOD; blockage of veins in the lungs); a stomach ulcer; heart, kidney or liver disease; a heart attack; an irregular heartbeat; a stroke; chest pain; high or low blood pressure; high cholesterol; a bleeding disorder; blood circulation problems; blood cell problems such as sickle cell anemia (a disease of the red blood cells), multiple myeloma (cancer of the plasma cells) or leukemia (cancer of the white blood cells); conditions affecting the shape of the penis (e.g., angulation, cavernosal fibrosis, or Peyronie's disease); or diabetes. Also tell your doctor if you or any of your family members have or have ever had an eye disease such as retinitis pigmentosa (an inherited eye condition that causes loss of vision) or if you have ever had sudden severe vision loss, especially if you were told that the vision loss was caused by a blockage of blood flow to the nerves that help you see.

• Tell your doctor if you have ever been advised by a healthcare professional to avoid sexual activity for medical reasons or if you have ever experienced chest pain during sexual activity. Sexual activity may be a strain on your heart, especially if you have heart disease. If you experience chest pain, dizziness or nausea during sexual activity, call your doctor immediately and avoid sexual activity until your doctor tells you otherwise.

After you are prescribed, tell all your healthcare providers that you are taking sildenafil. If you ever need emergency medical treatment for a heart problem, the healthcare providers who treat you will need to know when you last took sildenafil.²⁰

Grapefruit juice and products may interact with sildenafil, leading to unwanted side effects. Avoid the use of grapefruit products. Talk to your doctor about eating grapefruit and drinking grapefruit juice while taking this medicine.²¹

Sildenafil for erectile dysfunction is taken as needed, not on a regular dosing schedule, so you are unlikely to miss a dose.²²

Sildenafil may cause side effects. Tell your doctor if any of these symptoms are severe or do not go away:

• Headache

• Heartburn

• Diarrhea

• Flushing (feeling of warmth)

• Nosebleeds

• Difficulty falling asleep or staying asleep

• Numbness, burning or tingling in the arms, hands, feet or legs

• Muscle aches

• Changes in color vision (seeing a blue tinge on objects or having difficulty telling the difference between blue and green)

• Sensitivity to light

Some side effects can be serious. If you experience any of the following symptoms, call your doctor immediately:

• Sudden severe loss of vision (see below for more information)

• Blurred vision

• Sudden decrease or loss of hearing

• Ringing in ears

• Dizziness or lightheadedness

• Fainting

• Chest pain

• Worsening shortness of breath

• Erection that is painful or lasts longer than four hours

• Itching or burning during urination

• Rash

Some patients experienced a sudden loss of some or all their vision after they took sildenafil or other medications that are similar to sildenafil. The vision loss was permanent in some cases. It is not known if the vision loss was caused by the medication. If you experience a sudden loss of vision while you are taking sildenafil, call your doctor immediately. Do not take any more doses of sildenafil or similar medications such as tadalafil (Cialis) or vardenafil (Levitra) until you talk to your doctor.

There have been reports of heart attack, stroke, irregular heartbeat, bleeding in the brain or lungs, high blood pressure and sudden death in men who took sildenafil for erectile dysfunction. Most, but not all, of these people had heart problems before taking sildenafil. It is not known whether these events were caused by sildenafil, sexual activity, heart disease or a combination of these and other causes. Talk to your doctor about the risks of taking sildenafil.

Some patients experienced a sudden decrease or loss of hearing after they took sildenafil or other medications that are similar to sildenafil. The hearing loss usually involved only one ear and did not always improve when the medication was stopped. It is not known if the hearing loss was caused by the medication. If you experience a sudden loss of hearing, sometimes with ringing in the ears or dizziness, while you are taking sildenafil, call your doctor immediately. If you are taking sildenafil (Viagra®) for erectile dysfunction, do not take any more doses of sildenafil (Viagra®) or similar medications such as tadalafil (Cialis®) or vardenafil (Levitra®) until you talk to your doctor.

Sildenafil may cause other side effects. Call your doctor if you have any unusual problems while you are taking this medication.

If you experience a serious side effect, you or your doctor may send a report to the Food and Drug Administration's (FDA) MedWatch Adverse Event Reporting program online (http://www.fda.gov/Safety/MedWatch) or by phone (1-800-332-1088).²³

Keep this medication in the container it came in, tightly closed, and out of reach of children. Store the tablets at room temperature and away from excess heat and moisture (not in the bathroom). Store the suspension at room temperature or in a refrigerator, but do not freeze it. Dispose of any unused suspension after 60 days.

It is important to keep all medication out of sight and reach of children, as many containers (such as weekly pill minders and those for eye drops, creams, patches, and inhalers) are not child-resistant and young children can open them easily. To protect young children from poisoning, always lock safety caps and immediately place the medication in a safe location,­ one that is out of their sight and reach. Learn more at http://www.upandaway.org.

Unneeded medications should be disposed of in special ways to ensure that pets, children, and other people cannot consume them. However, you should not flush this medication down the toilet. Instead, the best way to dispose of your medication is through a medicine take-back program. Talk to your pharmacist or contact your local garbage/recycling department to learn about take-back programs in your community. See the FDA's Safe Disposal of Medicines website (http://goo.gl/c4Rm4p) for more information if you do not have access to a take-back program.²⁴

In case of overdose, call the poison control helpline at 1-800-222-1222 or emergency services (911) if the person collapses, has a seizure, has trouble breathing or cannot be awakened.²⁵

Do not let anyone else take your medication. Ask your pharmacist any questions you have about refilling your prescription.

It is important for you to keep a written list of all the prescription and nonprescription (over-the-counter) medicines you are taking, as well as any products such as vitamins, minerals, or other dietary supplements. You should bring this list with you each time you visit a doctor or if you are admitted to a hospital. It is also important information to carry with you in case of emergencies.²⁶

For treatment of erectile dysfunction or premature ejaculation, sildenafil’s brand name is Viagra®. When prescribed for pulmonary arterial hypertension, it is called Revatio®.²⁷

We offer a variety of prescription medication options for premature ejaculation including:

• Sertraline (Generic Zoloft®)

• Paroxetine (Generic Paxil®)

• Viagra®

• Cialis®

• Tadalafil (Generic Cialis®)

• Lidocaine Topical Desensitizing Cream

We offer a variety of prescription medication options for erectile dysfunction including:

• Tadalafil (Generic Cialis®)

• Avanafil (Generic Stendra®)

• Vardenafil (Generic Levitra®)

• Viagra®

• Cialis®

¹ MedlinePlus
² National Library of Medicine
³ Mayo Clinic
⁴ MedlinePlus
⁵ National Library of Medicine
⁶ Mayo Clinic
⁷ Mayo Clinic
⁸ Mayo Clinic
⁹ Healthline
¹⁰ Drugs.com
¹¹ Drugs.com
¹² MedlinePlus
¹³ National Health Service
¹⁴ National Library of Medicine
¹⁵ Healthline
¹⁶ Mayo Clinic
¹⁷ Cleveland Clinic
¹⁸ WebMD
¹⁹ Healthline
²⁰ MedlinePlus
²¹ Drugs.com
²² Drugs.com
²³ MedlinePlus
²⁴ MedlinePlus
²⁵ MedlinePlus
²⁶ MedlinePlus
²⁷ MedlinePlus