The Food and Drug Administration on Thursday said a major Canadian drug distributor was selling unapproved and mislabeled medicines to unsuspecting Americans looking to save money on prescriptions, and warned it to stop.

The company, CanaRx, sells many common prescription medicines at a lower cost to hundreds of public and private employer programs in the United States. Many of its buyers are city and county governments seeking to save money, among them: Albany, N.Y. and Duluth, Minn. CanaRx says the medications it sells are high-quality, from Canada, Australia and Britain, but the F.D.A. said this is not always the case.

“Operations like CanaRx use their names to imply that patients are receiving medicines approved in Canada, when it’s likely that some of those drugs are from other countries with lax standards,” Dr. Scott Gottlieb, the F.D.A. commissioner, said in an interview. “Such operations take advantage of unsuspecting Americans, by purporting to distribute safe and effective imported drugs, at least some of which are instead expired, mislabeled, subject to recalls or potentially counterfeit.”

A statement posted on the agency’s website urged consumers not to use any medicines obtained from CanaRx.