Viagra is chemically sildenafil citrate and is best known for treating erectile dysfunction. The drug was initially marketed as a high blood pressure and angina relieving medication, but quickly acquired superstar status because of its ability to treat erectile dysfunction in a satisfactory manner.

Viagra's history is also interesting. The little blue pill was being trialed as an angina medication at an England research facility owned by Pfizer. Wile the drug had little or no effect on angina, researchers noted that it induced marked penile erections. Pfizer patented Viagra in 1996 and had it on the market two years afterward.

However it has not been plain sailing for Viagra. The drug is associated with some serious side effects including deafness. But it is also used in treating other diseases, most notably pulmonary hypertension.

Pulmonary hypertension is a condition where persistent high blood pressure in the arteries of the lungs leads to right heart failure and eventually death. Last month it was reported that a two-year-old British boy needed Viagra to treat his pulmonary hypertension.

According to the National Institutes of Health, some side effects associated with Viagra include:
    * Headache
    * Upset stomach
    * Diarrhea
    * Dizziness or lightheadedness
    * Flushing (feeling of warmth)
    * Stuffy nose

But these have not deterred men from taking to the little blue pill in a big manner. Some 35 million men have used the drug at some point of time, while Pfizer has sold over 1 billion little blue pills to date. More than anything Viagra has demonstrated that it has staying power in a market where drugs are daily consigned to the pages of history.