Viagra (Sildenafil Citrate) is a prescription drug used to treat erectile dysfunction). Viagra was developed and is marketed by Pfizer. Viagra acts phosphodiesterase type 5 (PDE5) inhibitor, an enzyme that regulates blood flow in the penis.
Since becoming available in 1998, Viagra has been the prime treatment for erectile dysfunction; Viagra’s primary competitors on the market are Cialis and Levitra. Viagra is frequently called the ‘blue pill’.
However Viagra does not work without sexual stimulation, because of lack of activation of the NO/cGMP system, Viagra should not cause an erection.