Effexor and generic version venlafaxine hydrochloride are used to treat major depressive disorder. Now it is likely that the drug will become more widely available to improve the mood of patients and the morale of Barr Pharmaceutical (NYSE:BRL) shareholders as well. In a particularly favorable announcement for shareholders of the stock, the drugmaker announced yesterday that its subsidiary PLIVA has received tentative FDA approval for its generic version of Wyeth's (NYSE:WYE) Effexor.

For Fools with a long-term investing time horizon, this potential addition to Barr's portfolio could prove extremely beneficial to the company's bottom line. In 2006, Effexor was Wyeth's top-selling drug, with $3.7 billion in sales. The FDA approved the first generic version of Effexor for sale in the U.S. only 11 months ago. The approval was granted to Israel-based Teva Pharmaceuticals (NASDAQ:TEVA). Given its high hopes for venlafaxine, Teva went north of the border, making its generic Effexor one of the largest launches in Canadian pharmaceutical market history.

The arrival of generic Effexor has had an almost immediate impact in the market. An 11% increase in Wyeth's Q4 sales of Effexor was followed by a 6% decrease in Q1 sales of the drug, with the company attributing the slip to the recent emergence of generic competition.

The total market for venlafaxine hydrochloride tablets had annual sales of approximately $182.8 million for the 12 months ending April 2007, according to IMS sales data. Given that Teva was permitted to sell the drug in the U.S. for only a portion of 2006 and was eligible for generic exclusivity, one could expect this amount to increase significantly on a year-over-year basis -- especially if Barr were to enter the picture. The long-term impact could also be significant for Barr's generic product sales, which increased 12% to $839 million for its FY 2006. Generics accounted for approximately 65% of the company's FY 2006 sales.

It will be some time before Barr shareholders are able to reap the rewards of this development. The exclusivity attached to the patent protecting Effexor isn't scheduled to expire until June of next year, at which time Barr anticipates receiving final approval and commencing its marketing of the product in the U.S.

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Fool contributor Billy Fisher does not own shares of any of the companies mentioned. The Fool has a disclosure policy.