bioidentical hormone replacement therapy Bio-identical hormones are exact duplicates of those that are natural to, or occurring in the human body. Natural or bio-identical have to do with the chemical structure of a hormone and not it’s source. Synthetic hormones are not found in humans, and are not identical in structure or function to the bio-identical hormones they are intended to replace. Natural hormones are obtained from sterol analogues found in many varieties of plants, primarily soybean and wild yam. These estrogen and progesterone-like compounds are then transformed in the laboratory to the human bio-identical natural hormones.