Sepracor ( SEPR) said Tuesday that it will delay marketing of its new insomnia drug Lunesta by as much as two months. The company said the delay is caused by the federal government's need to "formally classify" the drug as a controlled substance. The Drug Enforcement Administration's "administrative process" for classifying the drug "is not yet complete," the company said. Lunesta was approved by the Food and Drug Administration on Dec. 15. At the time, Sepracor predicted the drug would be available in early January. Now, the Marlborough, Mass.-based company said it expects the drug will be on the market during the first quarter. "All commercial activities, including manufacturing, supply chain and sales and marketing required for a successful launch, are firmly in place," said W. James O'Shea, president and chief operating officer. The announcement sent the company's shares down $1.53, or 2.5%, to $58.62. Analysts cheered Sepracor after the company secured FDA approval of a drug that they view as a strong competitor to market leader Ambien, which is made by Sanofi-Aventis ( SNY). They noted that Lunesta doesn't have the same restrictions as Ambien. Lunesta's label lacks the recommendation that the drug's use be limited to seven to 10 days. Ambien's label contains that restrictive language.