Cenestin contains horse (equine) estrogens and some estrogens also found in humans, mostly estrone, I think which is weaker than estradiol. Studies have found these types of estrogens, because they contain equine estrogen to have a greater effect on coagulation factors and be a greater risk factor. For this reason, it is extremely rare these days to have this be prescribed to transsexual women and ciswomen as well. I would talk to your doctor and ask for the bio-identical kind, safer and just as effective.