Published: Sep 01, 2010 4:47 PM EDT
Updated: Sep 01, 2010 1:47 PM EDT

WASHINGTON (AP) - Allergan says it will pay $600 million to settle a years-long federal investigation into how it marketed its top-selling drug Botox.

The company says it will plead guilty to one misdeameanor charge of "misbranding," in which the company's marketing led physicians to use Botox for unapproved uses. Those uses included the treatment of headache, pain, spasticity and cerebral palsy.

It says it will pay $375 million in connection with the plea.

In addition, the company will pay $225 million in civil fines related to the investigation, though the company denies liability.

The Department of Justice began investigating Allergan's marketing in 2000. In recent years, federal investigators have reached multi-billion dollar settlements with Pfizer, Eli Lilly and other drug companies over drug marketing practices.