Two U.S. senators last week asked the Department of Health and Human Services’ Office of Inspector General to investigate high drug prices and any role played by health insurers’ shared ownership with the pharmacies that often fill the prescriptions.

“In functioning markets, generic drugs cost 80-85% less than their name-brand equivalents, giving patients much-needed relief from high drug costs and saving taxpayer dollars,” Sens. Elizabeth Warren, D-Mass., and Mike Braun, R-Ind., wrote in a letter. “But patients — including patients in public health-care programs like Medicare and Medicaid — who either use or are compelled to use vertically integrated specialty pharmacies are not seeing this relief.”