Since November 1993, recombinant bovine somatotropin (rbST), also called rBGH, has been sold to dairy farmers with FDA approval. Cows produce bovine growth hormone naturally, but some producers administer an additional recombinant version of BGH which is produced through genetically engineered E. coli to increase milk production. Bovine growth hormone also stimulates liver production of insulin-like growth factor 1 (IGF1). The U.S. Food and Drug Administration, the National Institutes of Health and the World Health Organization have reported that both of these compounds are safe for human consumption at the amounts present.