A GAO report found that foster children were being prescribed psychotropic drugs at rates as high as 13 times that of children in the general population. (Getty Images)

The senator who spurred the Government Accountability Office to investigate the startling numbers of foster children being put on powerful, mind-altering drugs is calling on the Obama administration to follow through on its vow to find solutions to the issue.

"This is a deeply disturbing problem that demands immediate attention," Sen. Tom Carper, D-Del., wrote in a letter to Health and Human Services Secretary Kathleen Sebelius and provided exclusively to "20/20." "…Unless our Medicaid policies properly reflect best medical practices, the result will be damaging to the program's financial bottom line but, more importantly, to the health and welfare of our nation's foster care children." ( See the full letter here.)

As "20/20? and "World News" reported during ABC News' own extensive investigation of the medication of foster children late last year, the GAO found that doctors prescribe psychotropic medications to foster children at a rate of up to 13 times that of children in the general population. The GAO investigation was launched at the request of the Senate Federal Financial Management Subcommittee, which is chaired by Carper.

Watch "20/20's" full report on overmedication in the foster care system here.

A spokesman for the Health and Human Services Department said that the agency received the letter yesterday and will be responding as soon as possible.