How do these compare to Premarin and other prescription drugs?
They do not compare. Premarin is a drug manufactured from PREgnant MARe uRINe, designed to force a specified amount of estrogen into the human body, whether that body can handle that much estrogen or not. Other prescription estrogen drugs also do the same job; the various forms are designed to try to avoid problems with metabolism, etc. Once in the blood-stream, estrogen is estrogen is estrogen, regardless of its initial form (herb or drug) into your body.