Professional information for Viagra

The following information is provided for clinicians and other healthcare professionals.


Viagra is approved to treat erectile dysfunction (ED) in males ages 18 years and older.


Viagra is taken orally. It should be taken between 30 minutes and 4 hours before planned sexual activity.

Viagra Mechanism of action

Viagra contains sildenafil citrate, an inhibitor of phosphodiesterase type 5 (PDE5). Viagra enhances the action of cyclic GMP, which is released in the penis in response to sexual stimulation. Cyclic GMP dilates smooth muscle in the penile tissue. It also increases blood to flow into the corpus cavernosum, causing an erection.

Viagra blocks PDE5 from breaking down cyclic GMP, thereby improving the ability to achieve and maintain an erection in response to sexual stimulation.

Pharmacokinetics and metabolism

Sildenafil has an average bioavailability of 41% (ranges from 25% to 63%) after oral administration of Viagra tablets.

When taken on an empty stomach, the time to reach peak plasma concentration (Tmax) is approximately 30 to 120 minutes. The median Tmax is 60 minutes. Taking Viagra with a high-fat meal delays Tmax by about 60 minutes. It also reduces the maximum plasma concentration (Cmax) by an average of 29%.

Sildenafil is primarily metabolized by hepatic CYP3A4, to a metabolite with similar activity to sildenafil. Sildenafil and its active metabolite have a terminal half-life of approximately 4 hours.

Approximately 80% of the dose is excreted in feces, and approximately 13% is excreted in urine.

Reduced clearance of sildenafil is seen in people ages 65 years and over, and in those with hepatic impairment or severe renal impairment.


Viagra is contraindicated in people with a known allergy to sildenafil, or any of the inactive ingredients in Viagra.

Viagra is also contraindicated for use in combination with:

  • nitrate drugs in any form, such as:
    • nitroglycerin (Nitromist, Nitro-Dur, Nitrolingual Pumpspray, Gonitro, others)
    • isosorbide mononitrate (Monoket)
  • guanylate cyclase stimulators, such as riociguat (Adempas)


Store Viagra at room temperature between 68oF and 77°F (20oC and 25°C).