As expected, the Food and Drug Administration has approved the first generic versions of Eli Lilly's (NYSE:LLY) depression drug Cymbalta.

Six versions in fact.

On Wednesday, Aurobindo Pharma, Dr. Reddy's Laboratories (NYSE:RDY), Lupin, Sun Pharmaceuticals, Teva Pharmaceuticals (NYSE:TEVA), and Torrent Pharmaceuticals all got the FDA's green light to sell the drug known generically as duloxetine.

Given the large number of generic versions, the companies are going to have to compete on price, leading to limited profits for the generic-drug makers and a sharp drop in sales of the branded product.

U.S. sales of Cymbalta were $1.1 billion in the third quarter. Despite the expiration coming toward the end of the quarter, the pharma expects U.S. sales will drop to just $500 million this quarter. Since the expiration of the U.S. patent exclusivity was widely known, wholesalers and retail pharmacies have likely reduced inventories in anticipation of the launches of the generic versions. Eli Lilly's estimated sales also includes expected returns of the product.

While the drop in sales of Eli Lilly's top-selling drug will affect revenue and profits, the exact date for the loss of exclusivity has been known for years and thus shouldn't affect the company's valuation at this point.

Fool contributor Brian Orelli has no position in any stocks mentioned. The Motley Fool recommends Teva Pharmaceutical Industries. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.