How Viagra Works

Mature men are discovering a newfound sexual youth because of the little blue pill called Viagra — which is used to treat erectile dysfunction (ED), or impotence, as it's often called. 

Let's learn more about Viagra, how it's dosed, and what to watch out for when a person has been prescribed this medication.

How It Works

Viagra (sildenafil) belongs to a group of medicines that delay the enzymes called phosphodiesterase from working too quickly. By controlling phosphodiesterase, sildenafil helps to maintain an erection that is produced when the penis is physically stimulated.

Prescription Guidelines

Viagra comes in tablet form in dosages of 25mg, 50mg, and 100mg. The generic form is 20 mg.

• Men Up to 65 Years of Age: Viagra 50mg by mouth is usually started. It's prescribed to be taken once a day, 30 minutes to 4 hours before intercourse. In situations where 50mg isn't effective, a person's healthcare provider may prescribe 100mg to be taken once daily 30 minutes to 4 hours before intercourse.
• For Men Older than 65 Years of Age: Often a lower dose is started, like 25mg. It's taken 30 minutes to 4 hours before sexual intercourse. In some circumstances, men older than 65 may have their doses increased. Taking Viagra on an empty stomach may make the drug more effective.

Important Caution: Under no circumstances should men increase their Viagra doses without first consulting their healthcare provider.

It's also important to be aware of interactions with heart or high blood pressure medications, which can be dangerous. Viagra and other phosphodiesterase medications — such as Levitra (vardenafil), Cialis (tadalafil), and Stendra (avanafil) — should never be taken with any form of organic nitrates or nitrites (e.g., nitroglycerine and amyl nitrite, used for angina), nor should they be taken along with guanylate cyclase stimulators (e.g., riociguat, used to treat high blood pressure in the lungs).

Men also should not take Viagra if they are also taking any other medication for high blood pressure, such as Revatio (a form of sildenafil) or other drugs. Because phosphodiesterase medications such as Viagra may lower blood pressure, they should be used cautiously in men with heart disease (e.g., angina, history of heart attack, stroke, or narrowing of the aorta).

When in doubt, discuss with your healthcare provider if it is safe for you to take Viagra.

Potential Side Effects

• Headache
• Heartburn
• Diarrhea
• Feeling of warmth
• Nosebleeds
• Nasal congestion
• Sleep disturbance
• Numbness, tingling, or burning in extremities
• Muscle aches
• Changes in color vision
• Sensitivity to light

Serious side effects that require a person to call their healthcare provider right away include blurry vision, loss of vision, fainting, dizziness, chest pain, difficulty breathing, difficulty hearing, ringing in ears, rash, pain when urinating, painful erection, or an erection that lasts more than 4 hours. 

Precautions

If you think you need Viagra, please see your healthcare provider and inquire about a workup and a prescription for your erectile dysfunction. Do not order Viagra online — the FDA warns about the potential harm of obtaining Viagra-like products through the Internet, as their safety has not been studied, and their ingredients may be harmful to the consumer.

Also, the use of Viagra may be associated with higher levels of unprotected anal sex with an HIV-positive partner, according to a 2002 study in AIDS. Practicing safe sex, regardless of whether you use Viagra, is critical for your own sexual health and the health of your partner. 

Erectile Dysfunction Doctor Discussion Guide

Get our printable guide for your next doctor's appointment to help you ask the right questions.

Download PDF

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