BOSTON – A company that distributed human growth hormone to “well known athletes and entertainers” has agreed to pay a $10.5 million penalty and cooperate with ongoing law enforcement investigations, federal prosecutors said yesterday.

Under the terms of the agreement, Specialty Distribution Services Inc., a subsidiary of Express Scripts Inc., will not face prosecution for three years if it fully complies with terms of the agreement.

Steve Littlejohn, a spokesman for St. Louis-based Express Scripts, said the company fully cooperated in the federal investigation and has already implemented procedures to prevent the illegal distribution of human growth hormone.

“Express Scripts does not condone the use of human growth hormone for anti-aging, cosmetic or performance enhancement purposes,” the company said in a news release.

Specialty Distribution Services “knowingly distributed human growth hormone to certain well known athletes and entertainers, including a well known athlete in Massachusetts, knowing that their intended use was athletic performance enhancement, cosmetic or anti-aging,” in violation of federal law, the U.S. attorney’s office said in a news release.

Prosecutors did not mention any names of those believed to have bought HGH from the firm.