Acorda Therapeutics (NASDAQ:ACOR) is trading down Monday on circulation of the September 2012 Formulary Decision Highlights from GroupHealth, a healthcare coordination cooperative. For ACOR’s lead product and primary revenue driver, Ampyra, the communication states that the drug provides outcomes of questionable clinical significance, and adds the criteria of “medical necessity review required” for prescribing Ampyra. It is widely known that Ampyra only helps about a third of patients treated and that the effects of the drug wane over time. Sales of Ampyra, annualizing at about $260 million, never reached the potential that many analysts expected, with some originally calling for $1 billion or more. Should insurance companies tighten their policies on Ampyra reimbursement, sales estimates for the drug may again need to be reduced. The news is an incremental negative, and the uncertainty could pressure the shares further.