Updated from 8:54 a.m. EDT
shares fell Thursday even though the company announced positive results of its treatment for children suffering from attention deficit hyperactivity disorder.
The Pennsylvania-based biotech company said results in three studies were "highly significant," prompting it to seek regulatory approval sooner than previously expected.
The company said one daily dosage of its new modafinil formulation "significantly improves symptoms" of ADHD.
Cephalon said it would file its application with the Food and Drug Administration in the fourth quarter of 2004, rather than the first quarter of 2005.
ADHD is one of the most common psychiatric disorders among children, resulting in inattention, hyperactivity, and impulsivity.
Cephalon's modafill has already been approved for use in treating excessive sleepiness associated with narcolepsy, obstructive sleep apnea and shift work sleep disorder.
Shares fell 38 cents, or 0.8%, to $45.07.