I have used bio-identical hormones for approximately 35 yrs. The synthetic progesterone caused acne and did not alleviate my other symptoms. When I was put on Synthroid for my thyroid, I had a racing heart, rashes, and intestinal issues. I overdosed on Prometrium and synthetic Synthroid. Since on natural progesterone, estrogen, and armor thyroid or T3/T4 all the other symptoms are gone. I have managed my health much better through natural means without all the side effects from synthetic drugs minus all the other prescriptions for the symptoms the synthetic(unnatural) drugs cause. My body and mind are good, now. Dr's say Synthroid is natural, no it is not.. It is synthetic. My body does not like it!! My body knows what it needs and responds accordingly and has negative reactions to unnatural drugs. The dosage can also be made to what I need not a pre-stamped dosage that is incorrect for my body. My body, My choice.