A Florida oncologist was charged Thursday with giving cancer patients medications, included chemotherapy drugs, from other countries that were not approved by the federal Food and Drug Administration.

Federal health officials said patients at East Lake Oncology in Tampa were unaware that for the past six years Dr. Diana Anda Norbergs and her staff were giving them cheaper, misbranded drugs that weren't registered or approved for use in the United States. She then billed the taxpayer-funded Medicare program and private insurance companies for the illegal prescriptions, claiming that she was actually using the FDA-approved versions. Norbergs pocketed the extra money, according to the indictment first reported by The Associated Press.

"The purity and efficacy of these drugs were of the utmost importance for patient care," prosecutors said in the indictment.

Norbergs is charged with 12 counts of health care fraud and nine counts of receiving misbranded drugs in interstate commerce.

Her website, which includes glowing testimonials from patients, says she is retired but does not indicate when that occurred. "Dr. Norbergs truly loves what she does and is grateful for the opportunity to help and take care of people," according to the website.

The Associated Press was unable to find a telephone listing for her home Thursday, and the number at her former business gave a busy signal. She was expected to have her first appearance before a judge later Thursday.

Some of the drugs that she purchased from other countries were also sold in the U.S. under different names, authorities said. Many of the drugs were given through an IV. Authorities said Norbergs typically purchased the drugs from the United Kingdom and Canada and also instructed her staff to purchase the discounted drugs from foreign distributors.

"Allegations don't get much more serious than this, that a physician gave unapproved, discounted drugs to her cancer patients without their knowledge and billed Medicare as if she had provided more costly FDA-approved drugs," said Shimon R. Richmond, special agent in charge of the U.S. Department of Health and Human Services Office of Inspector General. "The crimes alleged here violate laws meant to protect the health of patients, in this case patients fighting cancer, as well as the integrity of the Medicare program."

Authorities are reaching out to patients who have been treated at East Lake Oncology since 2009 and may have unknowingly received the misbranded drugs. It's unclear what impact, if any, the drugs may have on their health.