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What Is Viagra? Side Effects, Usage, Dosage & More

By Chesney Fowler, MD bool(true)
Medically reviewed
April 8, 2021

Viagra is a brand-name prescription drug approved by the Food and Drug Administration (FDA) to treat erectile dysfunction (ED) in men. It contains sildenafil citrate, one of four phosphodiesterase-5 inhibitors (PDE5 inhibitors) that helps men who have trouble achieving or sustaining an erection by increasing blood flow in their penis.

Sildenafil is also marketed under the brand name Revatio to help people with pulmonary arterial hypertension (PAH, a form of high blood pressure) participate in physical activities.

Men with erectile dysfunction struggle to achieve or maintain an erection long enough to engage in satisfying sexual activity. The condition is the most common sexual dysfunction in men, becoming more prevalent among men as they age. By the time they reach 70, roughly 70% of men will develop ED.

Pfizer initially developed Viagra in the hopes that it would help treat cardiovascular conditions like angina pectoris, a type of chest pain caused by heart disease. While studying the medication, though, researchers found that Viagra had unexpectedly positive effects on men who had ED. When they took the “little blue pill” about an hour before sexual stimulation, they were able to get an erection and keep one long enough to enjoy a sexual experience.

When Viagra was FDA-approved in 1998, it revolutionized how healthcare providers treat erectile dysfunction. Since that time, Viagra has been prescribed for more than 64 million men worldwide. 

What Is Viagra?

Viagra is a brand-name prescription drug that treats erectile dysfunction (ED) in men. It contains sildenafil citrate, a phosphodiesterase-5 inhibitor (PDE5 inhibitor) that blocks a particular enzyme from breaking down a molecule called cyclic guanosine monophosphate (cGMP).

cGMP helps the smooth muscles around the arteries in your penis relax so that more blood vessels can flow into it during periods of sexual stimulation.

By blocking the enzyme that breaks it down, Viagra increases the amount of cGMP in the body, improving blood flow and helping men more easily achieve an erection.

Viagra is one of four brand-name prescription PDE5 inhibitors on the market today. The others are Cialis (tadalafil), Levitra (vardenafil), and Stendra (avanafil). Viagra is also available in its identical, generic form called sildenafil. 

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What Is Viagra Used For?

Viagra is used to treat males with erectile dysfunction (a.k.a. impotence). Erectile dysfunction is when a man can’t get or sustain an erection firm enough to enjoy sexual activity. It is a widespread condition, one that often affects men as they age. 

When men become sexually aroused, the brain and nervous system send signals to the penis that tell smooth muscles around its arteries to relax and widen. That, in turn, allows more blood to flow into the penis tissues, filling them with blood until the penis becomes fully erect.

Because sexual arousal involves so many different processes—the brain, heart, emotions, nerves, muscles, and more—there can be several reasons why a person develops erectile dysfunction.

Some men suffer from physical conditions that inhibit their sexual responses, like diabetes, heart disease, Peyronie’s disease, or prostate issues. Others may develop erectile dysfunction because of a combination of physical and psychological problems like stress or anxiety that can cause difficulty achieving or maintaining an erection. 

Side Effects

Many men with ED benefit from Viagra because it helps increase blood flow to their penis during sexual activity. As with any medication, though, Viagra comes with potential downsides. Common mild to moderate side effects include: 

  • Headache, muscle ache, or back pain
  • Warm or red skin
  • Flushing skin or rash
  • Stomach upset or nausea
  • Diarrhea
  • Eye problems, including light sensitivity or blurred vision 
  • A stuffy, bloody, or runny nose 
  • Dizziness 
  • Sneezing
  • Tenderness around the eyes
  • Difficulty sleeping (insomnia)

Less commonly, men have reported bladder pain, a burning feeling in their chest or stomach, tingling skin, cloudy or bloody urine, painful urination, or tenderness in their stomach area. 

Occasionally people may experience more serious side effects, including:

  • Difficulty breathing
  • Clumsiness or unsteadiness
  • Ear pain 
  • Buzzing or ringing in the ears
  • Redness, swelling, or sores on the mouth, tongue, or lips
  • Rectal bleeding
  • Trembling and shaking 
  • Vomiting 
  • Exhaustion

Some men experience fewer or less severe side effects over time as their body gets used to the medication. If you experience side effects and your symptoms persist or worsen, seek medical advice. If you or someone you know has taken Viagra and experiences an erection that is painful or lasts more than four hours, vision loss, or hearing loss, call your healthcare provider or head to the nearest emergency room. 

How to Take Viagra

Every person is different, so it’s important to talk to your doctor about the dosage and routine that’s right for you. Viagra comes in 25-milligram (mg), 50-mg, and 100-mg tablets.

Typically doctors prescribe the 50-mg dose, though your dosage may differ depending on your health history.

mNo matter what dose your doctor prescribes, never take more than one tablet in 24 hours. Taking more than the recommended amount of Viagra may increase the chances of developing serious side effects. 

Most people take Viagra 30 minutes to an hour before sexual activity. It’s best to take on an empty stomach; if you take Viagra after eating a high-fat meal, it may take it longer for you to experience its full effects. 

In order to achieve an erection, Viagra must be combined with sexual stimulation. The effects last between 4-5 hours, but your erection should not. If your erection lasts for more than four hours, call your doctor or go to the emergency room. 

Healthcare professionals recommend storing Viagra at room temperature in a dry place away from excess humidity or heat. Do not store Viagra near other medications or in the bathroom. 

Viagra is only FDA-approved to treat erectile dysfunction in men. It is not approved to treat sexual dysfunction in women. 

Precautions

Viagra can cause health complications in people with certain pre-existing conditions and interact poorly with some medications. Tell your doctor about any current health conditions, prescription medications you take, and over-the-counter medicines, herbal supplements, or street drugs you may use. Especially be sure your doctor knows if you have:

  • A history of heart problems, heart attack, or stroke
  • Chest pain (angina)
  • Irregular heartbeat
  • Low blood pressure
  • Any other cardiovascular condition
  • Pre-existing eye conditions such as retinitis pigmentosa and non-arteritic anterior ischemic optic neuropathy (NAION)

Do not take Viagra if you take nitrates for chest pain or alpha-blockers for blood pressure. These drug interactions may cause your blood pressure to drop suddenly and severely.

Taking Viagra when you have Peyronie’s disease, sickle cell anemia, or cavernosal fibrosis can put you at an increased risk for developing an erection that lasts more than four hours (priapism). If you experience a prolonged or painful erection and do not treat it quickly, you may damage your penis or cause permanent impotence. 

Drug Interactions

Certain medications, supplements, and street drugs can interact poorly with Viagra. If you take these medications while taking Viagra, you may increase your risk of developing serious side effects and other health complications from the drug interactions. 

Some of the medications that interact poorly with Viagra include:

  • Amyl nitrite 
  • Isosorbide mononitrate 
  • Isosorbide dinitrate 
  • Itraconazole
  • Ketoconazole
  • Nitroglycerin
  • Nitroprusside
  • Riociguat
  • Many HIV medications

Additionally, limit your alcohol intake when taking Viagra. Drinking excessively while on the medication can lower your blood pressure, increase your chances of getting a headache, and accelerate your heart rate. 

Cost of Viagra 

Viagra’s cost can vary widely depending on your insurance coverage, the dosage your doctor prescribes, and the pharmacy where you source the medication. If you’re interested in exploring cost-effective ways of purchasing Viagra, looking online can help you identify your options. 

Alternatives to Viagra: Cialis vs. Viagra vs. Levitra vs. Adcirca

Viagra was one of the very first erectile dysfunction medications of its kind. When the FDA approved it in 1998, the pill revolutionized ED treatment in the United States. 

Today, a few other FDA-approved phosphodiesterase inhibitors are on the market: Vardenafil (Levitra), tadalafil (Cialis, Adcirca), and avanafil (Stendra) all help men with ED achieve erections in basically similar but subtly different ways.

Vardenafil, or Levitra, is the most structurally similar to Viagra. It is more biochemically potent than Viagra because it is more effective at selectively blocking the enzymes that inhibit men from achieving an erection. Because vardenafil is more powerful, most men don’t need to take as much of it; that puts men at less risk of developing serious side effects.

Tadalafil is structurally different from Viagra and is not metabolized as quickly. Because it’s long-lasting, people with erectile dysfunction can take it hours before engaging in sexual activity. However, there is a greater chance for adverse drug interactions with other medications. Anyone who takes prescriptions or supplements should consult with their healthcare professional to avoid health complications. 

Lastly, Avanafil only needs to be taken 15 to 30 minutes before sex, depending on the dose. It lasts slightly longer than Viagra does—for about six hours—and data suggests it causes fewer side effects. On the downside, there is no generic avanafil on the market, so Stendra may be expensive.

Can You Buy Viagra Online?

You can buy Viagra online, so long as you have a prescription from a doctor.

If you would like to schedule a consultation about your erectile dysfunction, K Health provides a simple, accessible option for ED treatment.

Chat with a doctor on your phone to determine whether you are experiencing ED. Your doctor will then prescribe you medication, which can be picked up at a local pharmacy or shipped discreetly directly to you. They will also provide a longer-term care plan to help you manage your ED.

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Frequently Asked Questions

How long does Viagra last?
Viagra is taken an hour before sexual activity, and the effects typically 4-5 hours. However, your erection should not last that long. If you have an erection for more than four hours, call your doctor.
How does Viagra work?
Viagra is a phosphodiesterase-5 inhibitor (PDE5 inhibitor) that blocks a specific enzyme from breaking down the molecule cyclic guanosine monophosphate (cGMP). cGMP helps the arteries in your penis widen so that more blood vessels can flow into it during periods of sexual stimulation. By blocking the enzyme that breaks it down, Viagra improves blood flow and helps men more easily achieve an erection.
How long does it take for Viagra to work?
You should take Viagra about an hour before sexual activity. Remember that it’s ideally taken on an empty stomach because having a high-fat meal beforehand can slow its effects.
How much Viagra should I take the first time?
Only take the dose of Viagra that your doctor prescribes to you; any more, and you risk developing serious side effects. No matter what your dosage is, only take one tablet per 24-hour period.
K Health articles are all written and reviewed by MDs, PhDs, NPs, or PharmDs and are for informational purposes only. This information does not constitute and should not be relied on for professional medical advice. Always talk to your doctor about the risks and benefits of any treatment.

Chesney Fowler, MD

Dr. Fowler is an emergency medicine physician and received her MD from George Washington University. She completed her residency in emergency medicine at Christiana Care Health System. In addition to her work at K Health, Dr. Fowler is a practicing emergency medicine physician in Washington, DC.