Bi-Est Cream contains two forms of estrogen — estradiol and estriol. Estradiol is the much more potent of the two. For some women it can be beneficial to blend a gentler estrogen like estriol to reduce side effects. This combination of estrogen can be adjusted to precisely meet the needs of your body. If you have struggled with side effects when using estrogen patches or other forms of hormone therapy, Bi-Est may be a good option for you.