Premarin stands for Pregnant Mare's Urine. When I had my hysterectomy 5 years ago, my doctor wanted to put me on it. I did alot of research on it and told him absolutely not. I was on a synthetic patch for a while. I finally stopped all hormone replacement therapy. The only thing I have is hot flashes, which I tolerate. They have now found that HRP causes dementia. I'd rather deal with the hot flashes than risk all the side effects as well as put horses lives in jeopardy.