Science News
from research organizations

FDA Approves Impotence Pill, Viagra

April 1, 1998
Food And Drug Administration
The Food and Drug Administration has announced the approval of Viagra (sildenafil citrate), the first oral pill to treat impotence, a dysfunction that affects millions of men in the United States.

March 27, 1998 -- The Food and Drug Administration today announced theapproval of Viagra (sildenafil citrate), the first oral pill totreat impotence, a dysfunction that affects millions of men inthe United States.

Unlike previously approved treatments for impotence, Viagradoes not directly cause penile erections, but affects theresponse to sexual stimulation. The drug acts by enhancing thesmooth muscle relaxant effects of nitric oxide, a chemical thatis normally released in response to sexual stimulation. Thissmooth muscle relaxation allows increased blood flow into certainareas of the penis leading to an erection.

Viagra was evaluated in numerous randomized, placebocontrolled trials involving more than 3000 men with varyingdegrees of impotence associated with diabetes, spinal cordinjury, history of prostate surgery, and no identifiable organiccause of impotence. Patients also had a wide range of otherconcomitant illnesses including hypertension and coronary arterydisease.

The drug's effectiveness was assessed primarily using a sexual function questionnaire. Patients were asked to report atthe beginning, and periodically throughout the studies, how oftenthey were able to achieve an erection adequate for intercourse, and how often that erection was maintained after penetration. Inaddition, patients kept diaries of their sexual histories. Inall trials, men on Viagra reported success more often than didmen on placebo, and rates of success increased with dose. Thefindings were consistent in men representing a wide range ofseverity and etiology of their erectile dysfunction (impotence). Men with diabetes or radical prostate surgery had somewhat lessimprovement than did other groups.

The recommended dose is 50mg taken one hour before sexualactivity; individuals may need more (100mg) or less (25 mg) and dosing should be determined by a physician depending oneffectiveness and side effects. The drug should not be used morethan once a day.

The most common side effects reported in clinical trialsincluded headache, flushing, and indigestion, which occurred at aslightly higher rate in patients taking the drug than among thosetaking placebo. Some patients on Viagra (about 3 percent) alsoreported changes in vision, principally altered colorperception.

The drug should not be used with organic nitrates such asnitroglycerin patches or sublingual tablets because thecombination may lower blood pressure. The safety and efficacy of using Viagra with other treatments for impotence has not beenstudied, and the use of such combinations is not recommended.

Viagra confers no resistance to AIDS or other sexuallytransmitted diseases.

Before taking Viagra, patients are advised to:

  • Have a thorough medical history and physical examination todiagnose impotence, determine underlying causes and identifyappropriate treatment, and
  • discuss the cardiac risk associated with sexual activityprior to initiating any treatment for impotence.
Viagra is manufactured by Pfizer Pharmaceuticals, New York, NY. The product was approved by FDA in less than sixmonths after submission. The FDA's clinical review of thestudies, approval letter and labeling can be found on theinternet at

Story Source:

Materials provided by Food And Drug Administration. Note: Content may be edited for style and length.

Cite This Page:

Food And Drug Administration. "FDA Approves Impotence Pill, Viagra." ScienceDaily. ScienceDaily, 1 April 1998. <>.
Food And Drug Administration. (1998, April 1). FDA Approves Impotence Pill, Viagra. ScienceDaily. Retrieved May 7, 2017 from
Food And Drug Administration. "FDA Approves Impotence Pill, Viagra." ScienceDaily. (accessed May 7, 2017).