What is Bio-Identical Hormone Replacement Therapy and how does it differ from Synthetic Hormones? Simply stated, bio-identical hormones are identical to the hormones produced in the human body. Other hormones like, oral conjugated equine estrogens and synthetic progestin, are not used here, because their use has demonstrated an increased risk of cancer, blood clots, and strokes, as shown in the 2002, Women’s Health Initiative Trial. Bio-identical hormones on the other hand show, no increase in breast cancer or blood clots, as demonstrated by The French E3N Cohort Study.