By Nate Raymond

(Reuters) - Illinois' attorney general on Thursday sued Insys Therapeutics Inc, accusing it of deceptively marketing and selling an addictive fentanyl-based medication, intended to treat cancer pain, to doctors for off-label uses.

The lawsuit, filed by Attorney General Lisa Madigan in Cook County Circuit Court, comes as Insys faces a number of state and investigations involving its drug Subsys as U.S. authorities seek to combat a national opioid abuse epidemic.

"This drug company's desire for increased profits led it to disregard patients' health and push addictive opioids for non-FDA approved purposes," Madigan said in a statement.

Madigan, whose office is investigating other opioid manufacturers for similar practices, said the lawsuit seeks to bar Insys from selling its products in Illinois and impose financial penalties on the company.

Insys, based in Arizona, did not respond immediately to requests for comment.

Subsys, which Insys launched in 2012, is a spray approved for managing pain in cancer patients that contains fentanyl, a highly-addictive and regulated synthetic opioid. It generated $329.5 million in net revenue in 2015.

The lawsuit alleged that rather than marketing the drug to oncologists treating cancer patients, Insys instead illegally marketed it to doctors who prescribed high volumes of opioid drugs.

Madigan said Insys rewarded doctors nationally for prescribing Subsys for off-label uses through payments for sham speaking events and expensive restaurant dinners.

The case came after federal prosecutors in Manhattan in June brought charges against two former Insys employees for engaging in a scheme to pay doctors kickbacks including speaker fees to prescribe Subsys.

Those ex-employees, Jonathan Roper, a former Insys district sales manager, and Fernando Serrano, a former sales representative, pleaded not guilty last week.

The case is People of the State of Illinois v. Insys Therapeutics Inc, Cook County Circuit Court, Chancery Division, No. 2016CH11216.

(Reporting by Nate Raymond in New York; editing by Chizu Nomiyama, Bernard Orr)