Endo Pharmaceuticals is jumping into the industry's testosterone segment.

The Chadds Ford company said Wednesday that the Food and Drug Administration had approved its Fortesta Gel for low testosterone levels, whose symptoms include sexual dysfunction, down moods, fatigue, and osteoporosis.

Fortesta joins a field of three other gels to treat "Low T."

Auxilliam Pharmaceuticals Inc., of Malvern, has an entrant in the category, and its FDA-approved Testim gel produced $137.8 million in revenue for the nine months ended Sept. 30, according to its regulatory filing. The two other companies with Low T topicals are Abbott Laboratories and Eli Lilly & Co., an Endo official said.

Endo estimates that 14 million men in the United States suffer from Low T and that only about 1.3 million are being treated for it. The company did not provide an estimate for the potential revenue from Fortesta, which it has licensed from U.K.-based ProStrakan Group P.L.C.

Ivan Gergel, Endo's executive vice president of research and development, said Fortesta is applied daily to the inner thigh - two drops each thigh. The gel is odorless. According to the company, possible risks include lower sperm count if used in large doses and a higher risk of prostate cancer.

Men can use Fortesta for several months or longer. An Endo official said the company expected to begin selling Fortesta in the first quarter of 2011. Pricing has not been established.

Contact staff writer Bob Fernandez at 215-854-5897 or bob.fernandez@phillynews.com.