A federal government investigation into Questcor Pharmaceuticals Inc. could deal another blow to sales for its only product and main revenue source, H.P. Acthar gel, according to analysts who cover the company.

The Anaheim, Calif., drugmaker said Monday the U.S. government is investigating its promotional practices. The company’s announcement comes after health insurer Aetna Inc. recently said it will stop reimbursement for most uses of Acthar. Company shares plummeted last week after a research website reported Aetna’s decision.