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Last updated December 26, 2019. 3 minute read

How does Viagra work? How can it work for me?

It’s part of a family of drugs known as PDE-5 inhibitors. Viagra works by inhibiting a natural chemical that causes blood to flow out of an erect penis.

Self Written by Michael Martin
Reviewed by Dr. Mike Bohl, MD, MPH

Viagra (sildenafil) is an oral medication that treats erectile dysfunction (ED).

Sildenafil was originally developed to treat hypertension, a.k.a. high blood pressure. In clinical trials, it wasn’t effective at treating high blood pressure. However, it did do one thing: Men who took it got more erections. Approved by the FDA in March 1998, Viagra was the first oral medication approved to treat erectile dysfunction in the United States. Sildenafil is now also available as a medication called Revatio, which is used to treat pulmonary arterial hypertension, a rare type of high blood pressure in the lungs.

Viagra (sildenafil), Cialis (tadalafil), Levitra (vardenafil), and Stendra (avanafil) are all part of a family of drugs called PDE-5 inhibitors. PDE-5 (phosphodiesterase type-5) is an enzyme that breaks down a molecule called cGMP, resulting in vasoconstriction, or the narrowing of blood vessels.

Vitals

  • Viagra (sildenafil) is a medication prescribed to treat erectile dysfunction (ED).
  • It’s part of a family of drugs known as PDE-5 inhibitors.
  • Viagra works by inhibiting a natural chemical that causes blood to flow out of an erect penis.
  • Viagra has some common side effects, and people with certain health conditions shouldn’t use it.

How does Viagra work?

Erections may seem pretty basic, but they’re surprisingly complicated. Getting an erection involves cooperation between your heart, blood vessels, hormones, nerves, and even your mood. During an erection, cGMP causes tissues in the penis to relax. As a result, blood flows into the penis and is trapped—up to eight times more blood than when the penis is flaccid. Eventually, this trapped blood gets released, the erection subsides, and blood flow returns to normal. 

Viagra works by blocking PDE-5. When PDE-5 is blocked, cGMP does not get broken down. As a result, the tissues in the penis stay relaxed and engorged with blood.

Viagra is highly effective for erectile dysfunction, but it’s not a magic pill: You need to feel sexually aroused for it to work.

How long does Viagra take to start working?

Viagra starts working within 30 to 60 minutes, so you should take it at least that long before sexual activity. For some men, Viagra can start working more quickly.

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How long does Viagra last?

Viagra is effective for about two to three hours. It leaves the body completely within six to eight hours. Your personal mileage may vary, depending on your age, overall health, other medications, and dosage taken.

Are there any potential risks or side effects of taking Viagra?

Viagra and other ED medications can have side effects including headache, facial flushing, nasal congestion, stomach upset, back pain, and—rarely—temporary impaired color vision (men with the eye condition retinitis pigmentosa should check with their healthcare providers before using those prescriptions).

Also, in rare cases, Viagra can cause priapism, which is a painful erection that won’t go away. If an erection lasts more than a few hours, it can damage the penis. (That’s why ED medication has a warning about erections “lasting longer than four hours”). If you experience priapism or other serious side effects such as chest pain, severe headache, shortness of breath, fainting, or vision loss—basically anything majorly out of the ordinary—see a healthcare provider ASAP.

Some heart disease medications (such as nitrates) also increase nitric oxide in the body. Nitric oxide is a molecule that increases cGMP. As a result, taking ED meds with nitrates can be dangerous.

Viagra slightly lowers blood pressure. So if you already have low blood pressure, talk with your doctor before taking Viagra. Taking Viagra along with amyl nitrate (poppers) can lead to a dangerous, even fatal, drop in blood pressure.

What is ED?

Erectile dysfunction can include softer erections, erections that don’t last as long, less frequent erections, or even a lack of morning erections. ED isn’t just about not being able to get hard—it’s really more about how you and your partner feel about your sex life.

And it’s very common. Most guys experience ED at some point in their lives. In fact, more than 30 million men in the U.S. have dealt with erectile dysfunction. It’s important to address ED at the initial signs because it can also be a sign of a potentially serious condition like:

  • Heart disease
  • High blood pressure
  • Low testosterone
  • Diabetes
  • High cholesterol
  • Nerve damage
  • Depression
  • Sleep apnea

Read everything you need to know about erectile dysfunction here.

Safety of Viagra

Treatment with PDE-5 inhibitors is not safe for everyone. For example, people who take nitrates for certain heart conditions or the drug riociguat for the treatment of pulmonary arterial hypertension cannot take Viagra.

Certain lifestyle changes can also help with ED, including exercise, a better diet, and managing stress. Read more about all-natural ways to protect your erection here.

We understand: Talking about ED can be embarrassing. But you owe it to yourself to talk with a healthcare professional today. ED affects millions of men. Get the medical advice you need to take back control of your health.