This has been one of the advantages for Viagra?, in that it is capable of being taken as a tablet and is relatively quick-acting. A convenient factor when perhaps one's partner won't wait forever!

Viagra? dosages are usually 25mg to 100mg (50mg doses being the average), taken up to one hour before sexual intercourse. These dosages have produced side effects such as headache, flushing and dyspepsia. There have been some reports of disturbances, dizziness, and nasal congestion. Other rarer adverse effects reported include diarrhea, muscle pain, skin rashes, and urinary or respiratory-tract infection.

"Viagra was introduced in 1998 and since then it has been prescribed to over 16 million men," says David Glenn, one of the team that conducted the test tube experiments at Queen's University in Belfast, Northern Ireland. Taking Viagra could reduce men's fertility; suggest the results of a new study. The anti-impotence drug not only speeds sperm up, researchers found, but it also caused the vital reaction needed to penetrate an egg to occur prematurely.

Viagra and nitrates work by dilating the blood vessels, which, in turn, lowers blood pressure. Taken together, they can cause blood pressure to plummet to dangerous levels. The problem is compounded by Viagra's long-lasting effect. According to Charlotte Yeh, MD, chief of emergency medicine at New England Medical Center in Boston, "They [Viagra users] may not realize that Viagra remains active in the body for 12 hours or more."

Viagra is the most popular pill in the U.S., according to its manufacturer, Pfizer, Inc. Viagra has long been known to cause visual side effects and has now been linked to NAION, a ?stroke of the eye? that causes permanent loss of vision.