Just because a prescription is covered by insurance doesn’t mean that you’ll be paying less for them. In fact, you might be paying more, according to a New York Times/ProPublica report. The review found Americans may be overpaying for as much as one in every 10 prescriptions by using their insurance instead of seeking out an alternate source and paying cash.

The report said that the “shocking” revelation that individuals can do better for themselves than the drug prices negotiated by their insurers is revealing a problem that is far more complex than “the seemingly simple act of buying a bottle of pills.” It adds, “[A] host of players—drug companies, pharmacies, insurers and pharmacy benefit managers—are taking a cut of the profits, even as consumers are left to fend for themselves.”

There aren’t any national statistics to indicate just how often this becomes a problem, it points out, although it cites Michael Rea, chief executive of Rx Savings Solutions, estimating that the number may be as many as 10 percent of all drug transactions. “If true nationwide,” it adds, “that figure could total as many as 400 million prescriptions a year.”