Premarin is another source of estrogen. Estrogen is a generic term for a class of hormones, and there are many different types. The cream we prescribe has a 50:50 mixture of estriol and estradiol, two types of estrogens that naturally occur in your body.
Premarin (PREgnant MAre uRINe) is a mixture of several estrogens that are found in horses. Premarin is an older medication from a time when bioidentical hormones were not available. Estrogens from horses were commercially available substitutes, and although not a perfect match for humans, they were a reasonable alternative.
Bioidentical hormones, like what we use in our cream, tend to have fewer side effects and more benefits than Premarin. It's generally considered safer and more efficacious to increase the dose of bioidentical estrogens, rather than adding Premarin, if symptoms persist.