Viagra (Sildenafil) – Oral

What Is Viagra?

Viagra (sildenafil) is a prescription tablet used to treat erectile dysfunction, also known as impotence. It belongs to a group of medications called phosphodiesterase-5 enzyme (PDE5) inhibitors.

Viagra blocks an enzyme called phosphodiesterase type 5 (PDE-5), causing muscle relaxation and increased blood flow to the penis. By doing this, Viagra makes it easier to have and hold an erection.

Sildenafil is also available as a solution for intravenous injection under the brand name Revatio, which is used to treat pulmonary arterial hypertension. However, this article will focus on Viagra, the oral form of sildenafil, for erectile dysfunction.

Drug Facts

Generic Name: Sildenafil

Brand Name(s): Revatio, Viagra

Administration Route(s): Oral, Intravenous

Drug Availability: Prescription

Therapeutic Classification: Phosphodiesterase type 5 inhibitor

Available Generically: Yes

Controlled Substance: N/A

Active Ingredient: Sildenafil

Dosage Form(s): Tablet, powder for suspension, solution

What Is Viagra Used For?

The Food and Drug Administration (FDA) approved Viagra to treat the inability to get and keep an erection, also known as ED.

You will not get an erection just by taking Viagra itself. This medication helps with keeping an erection once sexually stimulated.

Sildenafil is also used to treat a kind of blood pressure that affects the arteries in the heart and lungs, called pulmonary arterial hypertension. The FDA approved sildenafil for this indication under the brand name Revatio.

Viagra (Sildenafil) Drug Information - Illustration by Zoe Hansen

Verywell / Zoe Hansen

How to Take Viagra

Take Viagra as ordered by your healthcare provider.

Generally, you can take it from anywhere between 30 minutes to four hours before planned sexual activity. However, you should aim to take the recommended dose one hour before sexual activity. You can take this medication with or without food. However, be aware that taking it with a high-fat meal can increase the time it takes to start working.

If you are not sure about how to use your medicine, talk to your provider. Do not take more than prescribed, as this can increase your chances of having harmful side effects.

Storage

The best temperature to store Viagra tablets is at room temperature. However, you may keep this drug between cool and regular hot temperatures (59 degrees and 86 degrees Fahrenheit) during trips.

Keep the tablets in a safe place, away from pets and children. Throw away any unused or expired drugs. Do not toss down the sink or toilet.  Ask your pharmacist about the best ways to toss your medicine. You can also check out take-back programs in your area.

Off-Label Uses

Healthcare providers may prescribe Viagra for off-label uses, meaning for conditions not specifically indicated by the FDA.

Viagra is used with other drugs to stop high-altitude pulmonary edema (a deadly form of high-altitude sickness). It also treats the Raynaud's phenomenon (decreased blood flow to specific areas of the body).

How Long Does Viagra Take to Work?

It takes about 60 minutes for Viagra to work. Taking it with a high-fat meal may delay its effects. If used for sexual dysfunction, Viagra's effects last for two to four hours once it begins to work.

What Are the Side Effects of Viagra?

This is not a complete list of side effects, and others may occur. A medical professional can advise you on side effects. If you experience other effects, contact your pharmacist or a medical professional. You may report side effects to the FDA at www.fda.gov/medwatch or 800-FDA-1088.

Common Side Effects

Common sides effects of Viagra include:

  • Muscle or back pain
  • Low blood pressure
  • Hearing loss
  • Nosebleed
  • Flushing
  • Heartburn
  • Trouble sleeping
  • Headache
  • Diarrhea
  • Stuffy or running nose
  • Nausea
  • Rash
  • Abnormal vision changes (changes in color vision or blurred vision)

Severe Side Effects

Viagra can cause serious side effects that are sometimes permanent.  Some of these side effects and their symptoms can include the following:

Call your healthcare provider immediately if you have a painful erection or erection lasting more than four hours. This is known as priapism, and it requires prompt medical treatment. Priapism can happen during sex and when you are not having sex.

Report Side Effects

Viagra may cause other side effects. Call your healthcare provider if you have any unusual problems while taking this medication.

If you experience a serious side effect, you or your provider may send a report to the FDA's MedWatch Adverse Event Reporting Program or by phone (800-332-1088).

Dosage: How Much of Viagra Should I Take?

Drug Content Provided and Reviewed by IBM Micromedex®

The dose of this medicine will be different for different patients. Follow your doctor's orders or the directions on the label. The following information includes only the average doses of this medicine. If your dose is different, do not change it unless your doctor tells you to do so.

The amount of medicine that you take depends on the strength of the medicine. Also, the number of doses you take each day, the time allowed between doses, and the length of time you take the medicine depend on the medical problem for which you are using the medicine.

  • For treatment of erectile dysfunction:
    • For oral dosage form (tablets):
      • Adults up to 65 years of age—50 milligrams (mg) as a single dose no more than once a day, 1 hour before sexual intercourse. Alternatively, the medicine may be taken 30 minutes to 4 hours before sexual intercourse. Your doctor may adjust your dose if needed.
      • Adults 65 years of age and older—25 mg as a single dose no more than once a day, 1 hour before sexual intercourse. Alternatively, the medicine may be taken 30 minutes to 4 hours before sexual intercourse. Your doctor may adjust your dose if needed.
      • Children—Use is not recommended.
  • For treatment of pulmonary arterial hypertension:
    • For oral dosage forms (suspension or tablets):
      • Adults—5 or 20 milligrams (mg) three times a day. Each dose should be taken about 4 to 6 hours apart.
      • Children—Use and dose must be determined by your doctor.

Modifications

Other medications may affect how Viagra works in your body. If you are also taking an alpha-blocker medication, such as Cardura (doxazosin) and Regitine (phentolamine), you may need a lower dose of Viagra. Talk to your healthcare provider about what other medications you take.

A lower starting dose of Viagra may also be considered if you are over 65 or have liver or kidney problems.

Missed Dose

Take Viagra only as needed and as directed by your healthcare provider. Do not take two Viagra doses at the same time or two doses on the same day.

Overdose: What Happens If I Take Too Much Viagra?

Overdose symptoms may include: 

  • Chest pain
  • Trouble breathing
  • Vision changes
  • Ringing in the ears

What Happens If I Overdose on Viagra?

If you think you or someone else may have overdosed on Viagra, call a healthcare provider or the Poison Control Center (800-222-1222).

If someone collapses or isn't breathing after taking Viagra, call 911 immediately.

Precautions

Drug Content Provided and Reviewed by IBM Micromedex®

It is important that you tell all of your doctors that you take sildenafil. If you need emergency medical care for a heart problem, it is important that your doctor knows when you last took sildenafil.

Do not use this medicine if you are also using a nitrate medicine, often used to treat angina or high blood pressure. Nitrate medicines include nitroglycerin, isosorbide, Imdur®, Nitro-Bid®, Nitro-Dur®, Nitrol® ointment, Nitrolingual® spray, Nitrostat®, and Transderm Nitro®. Some illegal ("street") drugs called "poppers" (such as amyl nitrate, butyl nitrate, or nitrite). Do not use this medicine if you also use riociguat (Adempas®).

If you will be taking this medicine for pulmonary arterial hypertension, your doctor will want to check your progress at regular visits. This will allow your doctor to see if the medicine is working properly and to decide if you should continue to take it.

If you take sildenafil for pulmonary arterial hypertension, do not take Viagra® or other PDE5 inhibitors, such as tadalafil (Cialis®) or vardenafil (Levitra®). Viagra® also contains sildenafil. If you take too much sildenafil or take it together with these medicines, the chance for side effects will be higher.

Sildenafil should not be used with any other medicine or device that causes erections.

It is important to tell your doctor about any heart problems you have now or may have had in the past. This medicine can cause serious side effects in patients with heart problems.

If you experience a prolonged or painful erection for 4 hours or more, contact your doctor immediately. This condition may require prompt medical treatment to prevent serious and permanent damage to your penis.

If you experience a sudden loss of vision in one or both eyes, contact your doctor immediately.

Check with your doctor right away if you have a sudden decrease in hearing or loss of hearing, which may be accompanied by dizziness and ringing in the ears.

If you already use medicine for high blood pressure (hypertension), sildenafil could make your blood pressure go too low. Call your doctor right away if you have more than one of these symptoms: blurred vision, confusion, dizziness, faintness, or lightheadedness when getting up from a lying or sitting position suddenly, sweating, or unusual tiredness or weakness.

This medicine does not protect you against sexually transmitted diseases (including HIV or AIDS). Use protective measures and ask your doctor if you have any questions about this.

Do not take other medicines unless they have been discussed with your doctor. This includes prescription or nonprescription (over-the-counter [OTC]) medicines and herbal or vitamin supplements.

What Are Reasons I Shouldn't Take Viagra?

People on nitrates (regularly or as needed) should not take Viagra. Taking Viagra with nitrates can cause very severe low blood pressure. Nitrates are medications used to treat chest pain. 

If you have chest pain while on Viagra, call 911 or go to your nearest emergency room. You must wait for at least 24 hours before taking your nitrate dose.

Do not take Viagra if you are allergic to it or any part of its formulation.

What Other Medications Interact With Viagra?

Taking Viagra with nitrates, alpha-blockers, and blood pressure medications can cause severely low blood pressure. You may need to avoid these medications altogether, or your healthcare provider may need to adjust your dose.

CYP3A4 inhibitors, such as ketoconazole or erythromycin, can increase the levels of Viagra exposure when taken together. You may need to start at a lower Viagra dose if you take any of these medications.

Tell your healthcare provider if you take the following:

  • Nitrates
  • Alpha-blockers, such as Hytrin (terazosin HCl), Flomax (tamsulosin HCl), among others
  • HIV protease inhibitors, such as Norvir (ritonavir)
  • Certain antibiotics, such as Biaxin (clarithromycin) or erythromycin
  • Blood pressure medications (antihypertensives)
  • Certain oral antifungal medications, such as ketoconazole
  • Other ED treatments

Some examples of the drugs to avoid while on Viagra are:

  • Nitrates, such as Noxivent (nitric oxide)
  • Edex (alprostadil)
  • Nipride (nitroprusside)
  • Adempas (riociguat)
  • Other PDE5 inhibitors
  • Revatio (sildenafil) or other PAH treatments containing sildenafil

What Medications Are Similar?

Similar drugs used to treat ED like Viagra include:

Levitra

Levitra has similar precautions, side effects, and effectiveness to Viagra. However, Levitra causes fewer vision problems.

Cialis

Cialis is also as effective and safe as Viagra. Although it has a mostly similar side effect profile to Viagra, it can cause minor eye problems. Cialis and Viagra both take the same amount of time to work. However, Cialis works longer than Viagra. For this reason, most people on ED drugs prefer Cialis to Viagra.

Stendra

Stendra also has a fast onset of action for erection. It begins to work in 15 to 30 minutes. It has similar side effects, effectiveness, and precautions with Viagra, but has fewer visual side effects.

Frequently Asked Questions

  • What is Viagra used for?

    Viagra treats the inability to get and keep an erection, also called erectile dysfunction (ED). 

  • How does Viagra works?

    Viagra works by relaxing your muscles and increasing blood flow to your penis. It helps you to get and maintain an erection once stimulated.

  • What should I do if I miss a dose of Viagra?

    Only take this medicine as needed before expected sexual activity. Do not take two doses, or two tablets, in one day.

  • How long does it take for Viagra to work?

    It takes about 60 minutes for Viagra to work and lasts two to four hours.

How Can I Stay Healthy While Taking Viagra?

Taking your medication as directed by a healthcare provider can help treat your ED. Try to remember to take your dose 30 minutes to one hour before sexual intercourse for the best results. If it does not work for you, let your provider know. Do not take two doses at a time. 

Call a healthcare provider immediately if you have an erection lasting more than four hours. You must get treated to prevent you from having future problems with having sex.

In addition to medical treatments, there are other ways you can cope with ED. Some people use other techniques for improving ED, such as sexual aids. Engaging in a healthy exercise and diet regimen can also help symptoms or keep them from getting worse.

Medical Disclaimer

Verywell Health's drug information is meant for educational purposes only and is not intended as a replacement for medical advice, diagnosis, or treatment from a healthcare professional. Consult your doctor before taking any new medication(s). IBM Watson Micromedex provides some of the drug content, as indicated on the page.

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4 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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  2. Smith BP, Babos M. StatPearls [Internet]. Sildenafil.

  3. Khera M. UpToDate. Treatment of male sexual dysfunction.

  4. Gong B, Ma M, Xie W, et al. Direct comparison of tadalafil with sildenafil for the treatment of erectile dysfunction: a systematic review and meta-analysis. Int Urol Nephrol. 2017;49(10):1731-1740. doi:10.1007/s11255-017-1644-5