Millions of retired Americans are leaving money on the table by failing to talk with their doctors about the possibility of switching to cheaper generic medicines, researchers at Medco said.

In a new study raising concerns that many retirees neglected to consider the cost of prescription drugs and other types of health care when planning their retirement, the researchers said these expenses have come as a shock to many seniors.

Among middle-income retirees, for example, the cost of prescription drugs alone consumes an average of 10% of each retiree's monthly income, they found.

But even when feeling the pinch, the study suggests that too many seniors fail to take action to stretch their prescription drug budgets.

"Nearly half of retirees stated they infrequently or never discuss with their doctors ways to save money on their medications," even though "research has shown that doctors are likely to prescribe generic drugs when asked by patients," the researchers said.