(3) Duff Wilson, As Generics Near, Makers Tweak Erectile Drugs; Testing the appeal of dissolvable and fast-acting versions. New York Times, Apr 14, 2011.
http://www.nytimes.com/2011/04/14/health/14pills.html?scp=1&sq=erectile&st=cse
("The third drug for erectile dysfunction to reach the market, Cialis, now eight years old, is racing ahead of the others [Viagra and Levitra] because of two ideas that have proven extremely popular: an everyday pill and a 36-hour 'weekender'")
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