Clinical safety of oral sildenafil citrate (VIAGRA) in the treatment of erectile dysfunction

Int J Impot Res. 1998 Jun;10(2):69-73; discussion 73-4. doi: 10.1038/sj.ijir.3900354.


Sildenafil citrate has been shown to be effective in a wide range of patients with erectile dysfunction and has been approved in the United States for this indication. The overall clinical safety of oral sildenafil, a potent inhibitor of phosphodiesterase type 5, in the treatment of erectile dysfunction was evaluated in more than 3700 patients (with a total of 1631 years of exposure worldwide). Safety and tolerability data were analysed from a series of double-blind, placebo-controlled studies and from 10 open-label extension studies of sildenafil in the treatment of erectile dysfunction. A total of 4274 patients (2722 sildenafil, 1552 placebo; age range 19-87 y) received double-blind treatment over a period of up to six months' duration, and 2199 received long-term, open-label sildenafil for up to 1 y. The most commonly reported adverse events (all causes) were headache (16% sildenafil, 4% placebo), flushing (10% sildenafil, 1% placebo), and dyspepsia (7% sildenafil, 2% placebo) and they were predominantly transient and mild or moderate in nature. These adverse events reflect the pharmacology of sildenafil as a phosphodiesterase type 5 inhibitor. No cases of priapism were reported. The rate of discontinuation due to adverse events (all causes) was comparable for patients treated with sildenafil (2.5%) and placebo (2.3%). In open-label extension studies, 90% of patients completed long-term sildenafil treatment, with only 2% withdrawing due to adverse events. Sildenafil is a well-tolerated oral treatment for erectile dysfunction.

Publication types

  • Clinical Trial
  • Randomized Controlled Trial
  • Research Support, Non-U.S. Gov't

MeSH terms

  • 3',5'-Cyclic-GMP Phosphodiesterases / antagonists & inhibitors*
  • Adolescent
  • Adult
  • Aged
  • Aged, 80 and over
  • Cardiovascular Diseases / chemically induced
  • Double-Blind Method
  • Dyspepsia / chemically induced
  • Enzyme Inhibitors / therapeutic use*
  • Erectile Dysfunction / drug therapy*
  • Flushing / chemically induced
  • Headache / chemically induced
  • Humans
  • Middle Aged
  • Piperazines / adverse effects
  • Piperazines / therapeutic use*
  • Placebos
  • Purines
  • Sildenafil Citrate
  • Sulfones


  • Enzyme Inhibitors
  • Piperazines
  • Placebos
  • Purines
  • Sulfones
  • Sildenafil Citrate
  • 3',5'-Cyclic-GMP Phosphodiesterases