What is Viagra?

Viagra is a brand-name prescription drug that’s approved to treat erectile dysfunction (ED). With ED, you’re unable to have or maintain an erection. Viagra is approved for this use in males ages 18 years and older.

Viagra contains the drug sildenafil. It belongs to a class of drugs called phosphodiesterase type 5 (PDE5) inhibitors. (A class of drugs is a group of medications that act in a similar way.) Viagra works by increasing blood flow to your penis, which helps you have and keep an erection. But this drug only works if you’re sexually aroused.

Viagra comes as tablets that are taken by mouth. In most cases, it should be taken about an hour before sexual activity, but it can be taken 30 minutes to 4 hours beforehand. Viagra is available in three strengths: 25 mg, 50 mg, and 100 mg.

Does Viagra work to treat ED?

Yes, it does. In several clinical studies, Viagra was effective in treating ED. In these studies, men who used the drug had an improved ability to have and keep erections that allowed for successful sex.

Across the studies, between 43% and 83% of men who took Viagra had improved erections. (These rates varied depending on the cause of their ED and the dosage of Viagra being used.) In comparison, improved erections occurred in 10% to 24% of men who took a placebo (no active drug).

To learn more about Viagra’s effectiveness, see the “Viagra uses” section below.

How long does Viagra last

You may wonder how long Viagra works when it’s used to treat erectile dysfunction (ED). Below, we answer questions related to how long Viagra works inside your body.

If you have other questions about how long Viagra works, talk with your doctor.

How long does Viagra take to work?

Viagra typically starts to work between 30 and 60 minutes after you take a dose of the drug. But Viagra itself doesn’t give you an erection. Instead, you’ll need to be sexually aroused in order for the drug to work.

Viagra keeps working in your body for up to 5 hours. This means that if you’re aroused, you should be able to achieve an erection for up to 4 hours after taking a dose of Viagra.

Even though Viagra keeps working in your body for several hours, your erection shouldn’t last this long. In fact, rarely, Viagra can cause priapism. With this condition, you have a long-lasting and sometimes painful erection.

Priapism is a medical emergency that needs to be treated right away. If it’s not treated, the condition can damage the tissues in your penis and cause irreversible erectile dysfunction (ED).

If you have an erection that lasts longer than 4 hours, go to the nearest emergency room or call 911.

What can I do to make Viagra work faster?

Viagra may work faster if you take it on an empty stomach. However, if Viagra is taken with food, especially with a high-fat meal, it will take longer to start working. And in this case, it could even be less effective for you.

How long will viagra stay in my system?

After taking a dose of Viagra, the drug’s level in your body will gradually decrease over a period of a few hours. You’ll have low levels of the drug in your body after about 4 hours. (And at this point, the drug won’t be working any longer.) But it can actually take about 24 hours for Viagra to be completely removed from your body.

Viagra side effects

Viagra can cause mild or serious side effects. The following lists contain some of the key side effects that may occur while taking Viagra. These lists don’t include all possible side effects.

For more information on the possible side effects of Viagra, talk with your doctor or pharmacist. They can give you tips on how to deal with any side effects that may be bothersome.

Note: The Food and Drug Administration (FDA) tracks the side effects of drugs it has approved. If you would like to report to the FDA a side effect you’ve had with Viagra, you can do so through MedWatch.

Mild side effects

Mild side effects of Viagra can include:*

  • headache
  • flushing
  • indigestion
  • mild and temporary vision changes, such as a blue tinge in your vision, blurred vision, and sensitivity to light
  • nasal congestion (stuffy nose)
  • back pain
  • muscle pain
  • nausea
  • dizziness
  • rash

Most of these side effects may go away within a few days or a couple of weeks. But if they become more severe or don’t go away, talk with your doctor or pharmacist.

* This is a partial list of mild side effects from Viagra. To learn about other mild side effects, talk with your doctor or pharmacist, or view the drug’s patient information.

Serious side effects

Serious side effects from Viagra aren’t common, but they can occur. Call your doctor right away if you have serious side effects. Call 911 if your symptoms feel life threatening or if you think you’re having a medical emergency.

Serious side effects and their symptoms can include:

  • Non-arteritic anterior ischemic optic neuropathy (NAION), which is an eye condition that causes damage to your optic nerve. Symptoms can include:
    • sudden decrease in vision in one or both of your eyes
    • sudden loss of vision in one or both of your eyes
  • Sudden decrease or loss of hearing. This condition may also involve other symptoms, such as:
    • tinnitus (ringing or buzzing in your ears)
    • dizziness

Other serious side effects, which are explained in more detail below in “Side effect details,” include:

  • allergic reaction
  • priapism (long-lasting and sometimes painful erection)
  • low blood pressure, if Viagra is taken with certain other medications
  • cardiovascular problems, such as heart attack, irregular heartbeat, or stroke, all of which occur mainly in people with heart disease

Side effect details

You may wonder how often certain side effects occur with this drugHere’s some detail on several of the side effects this drug may cause.

Allergic reaction

As with most drugs, some people can have an allergic reaction after taking Viagra. In clinical studies, less than 2% of people who took Viagra had an allergic reaction. It’s not known how often allergic reactions occurred in people who took a placebo (no active drug).

Symptoms of a mild allergic reaction can include:

  • skin rash
  • itchiness
  • flushing (warmth and redness in your skin)

A more severe allergic reaction is rare but possible. Symptoms of a severe allergic reaction can include:

  • swelling under your skin, typically in your eyelids, lips, hands, or feet
  • swelling of your tongue, mouth, or throat
  • trouble breathing

Call your doctor right away if you have a severe allergic reaction to Viagra. But call 911 if your symptoms feel life threatening or if you think you’re having a medical emergency.

Priapism

Rarely, Viagra can cause priapism, which is a long-lasting and sometimes painful erection. But it’s not known how often priapism occurs in men who take Viagra.

Priapism is a medical emergency that needs to be treated right away. If it’s not treated, the condition can damage the tissues in your penis and cause irreversible erectile dysfunction (ED).

If you have an erection that lasts longer than 4 hours, go to the nearest emergency room or call 911.

Low blood pressure

Viagra can temporarily lower your blood pressure after you take the drug. But this isn’t a problem for most people. In clinical studies, less than 2% of people who took Viagra had low blood pressure after taking the drug. It’s not known how often low blood pressure occurred in people who took a placebo (no active drug).

But keep in mind that a sudden drop in your blood pressure could be dangerous if you have certain heart conditions. Sudden low blood pressure may also be dangerous if you’re taking certain other medications.

For example, you shouldn’t take Viagra if you take nitrate medications to treat chest pain. You should also avoid taking Viagra if you take a drug called riociguat (Adempas). Taking Viagra with these medications can cause a dangerous drop in your blood pressure that leads to a heart attack or stroke.

If you have low blood pressure, taking Viagra could make you feel dizzy or lightheaded, or cause you to faint. You’re also more likely to have these problems if you take Viagra with certain drugs used to treat high blood pressure or enlarged prostate. If you feel dizzy or faint after taking Viagra, lie down until this feeling passes.

If you have a heart problem or low blood pressure, talk with your doctor about whether Viagra is safe for you.

For more information about taking Viagra with other medications, see the “Viagra interactions” section below. And for more information about taking Viagra if you have heart or blood pressure problems, see the “Viagra precautions” section below.

Heart attack, irregular heartbeat, and stroke

On rare occasions, some people taking Viagra have had a heart attack, stroke, or irregular heartbeat. These conditions mainly occurred in people who already had a heart problem. But sometimes these conditions occurred in people who didn’t have a heart problem. It’s not known for sure if Viagra caused the side effects.

If you have chest pain after taking Viagra, you should stop having sexual activity right away. But call 911 if your symptoms feel life-threatening, or if you think you’re having a medical emergency.

And if you have a heart problem, talk with your doctor before starting Viagra. They can discuss with you whether it’s safe for you to use this drug. For more information about taking Viagra if you have heart problems, see the “Viagra precautions” section below.

Headaches

Headaches are a common side effect of Viagra. Headaches, as well as flushing and dizziness, occur because Viagra widens certain blood vessels in your body. (The drug doesn’t just affect the blood vessels in your penis.)

In clinical studies, headaches were reported in 16% to 28% of people who took Viagra. (This percentage varied depending on the dose of Viagra used and how often the drug was taken.) In comparison, headaches were reported in 4% to 7% of people who took a placebo (no active drug).

If you have a headache after taking Viagra, it should go away fairly quickly. But if it’s bothersome, you can take a pain reliever containing acetaminophen or ibuprofen. Ask your doctor or pharmacist to recommend a medication that’s safe for you to use.

If you have a severe headache or a headache that won’t go away, call your doctor. They’ll help determine the best treatment for your headache.

Side effects in older men

Men ages 65 years and older tend to get higher levels of Viagra in their blood after taking a dose than younger men do. Having a higher level of the drug in your body could increase your risk of side effects. Because of this, older men have usually prescribed a dosage of Viagra that’s lower than the dosage given to younger men.

In clinical studies of Viagra, there weren’t any differences in side effects seen in men ages 65 years and older compared with those in men younger than 65 years.

If you have concerns about using Viagra given your age, talk with your doctor.

Erectile dysfunction (ED)

Taking Viagra doesn’t cause new or worsening ED. However, Viagra can sometimes cause priapism, which is a long-lasting and sometimes painful erection.

Priapism is a medical emergency that needs to be treated right away. If it’s not treated, priapism can damage the tissues in your penis and cause irreversible ED.

If you have an erection that lasts longer than 4 hours, you should immediately go to an emergency room or call 911.

How to relieve Viagra side effects

Most of the mild side effects of Viagra either tend to go away within a few hours of taking your dose or can be easily relieved.

For example, headaches, flushing, and dizziness can often be eased by lying down and resting. Avoiding alcohol will also help reduce these side effects. Headaches and sensitivity to light can also be improved by turning off any bright lights around you. If you have bothersome headaches with Viagra, ask your doctor or pharmacist to recommend a pain reliever that’s safe for you to use.

If you get indigestion after taking Viagra, try taking your dose of Viagra with a snack or light meal. Just be aware that if you do this, Viagra may take slightly longer to start working for you. (This is especially true if you eat a high-fat meal with your dose.) If your indigestion is bothersome, ask your doctor or pharmacist to recommend medication to help reduce your discomfort.

Also, keep in mind that certain side effects occur more often with higher doses of Viagra. These side effects include headaches, flushing, indigestion, nasal congestion, and changes in your vision. So if these side effects are a problem for you, talk with your doctor about taking a lower dosage of Viagra.

When to call your doctor

Don’t forget that some of Viagra’s rare side effects need immediate medical attention. For example, you should call your doctor right away if you have:

  • an erection that doesn’t go away and lasts for more than 4 hours
  • chest pain, dizziness, or nausea while you’re having sex, and these symptoms don’t go away when you stop having sex and begin to rest
  • sudden loss of vision in one or both of your eyes
  • sudden decrease or loss of hearing
Viagra generic

Generic versions of Viagra are available. A generic drug is an exact copy of the active drug in a brand-name medication. The generic is considered to be as safe and effective as the original drug. Generics tend to cost less than brand-name drugs.

Viagra contains the active drug sildenafil.

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