A study done in Brazil indicates a single dose of the erectile dysfunction drug Viagra may aggravate sleep apnea.

Sleep apnea, more common in men than women, occurs when breathing stops during sleep for 10 seconds or more due to an obstruction or narrowing of the airway in the nose, mouth or throat.

Researchers say it may be a contributing factor in the development of erectile dysfunction.

Published in the Archives of Internal Medicine, the Brazilian study examined the effects of a single 50-milligram dose of Viagra versus a placebo on 14 middle-aged men diagnosed with severe obstructive sleep apnea, WebMd reports.

The results indicated that even a single dose of Viagra lowered blood oxygen level and caused breathing to be more disordered.

Chief researcher Suely Roizenblatt says the results are only preliminary and further studies of the drug are needed to determine if it is risky.

Copyright 2006 by United Press International

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