Why Is There No Generic Premarin?

Generic Premarin: Why Isn’t There One?

Have you noticed there is no generic Premarin?  You probably never gave it any thought, most likely, until now. Knowing why there is no generic Premarin is revealing and says much about what had been the most commonly prescribed female hormone and the mainstay of hormone therapy.

For years Premarin has been used to treat menopausal symptoms like hot flashes and night sweats. Today, bioidentical estrogen therapy and progesterone therapy have slowly been replacing the use of Premarin, but Premarin remains commonly prescribed.

Once a drug goes off patent pharmaceutical companies can make generic versions of the patented name brand drug, but they have to show that their generic version is exactly identical to the brand name, in this case, Premarin. And, that’s where the problem is and the reason there is no generic Premarin.

Premarin: Natural for Horses but not Women

Now Premarin which first became available in 1942 has been off patent for years, so it is legally permissible for a drug company to make generic Premarin if they can show it to be identical to Premarin. And, that’s where the problem is.  Premarin is actually a group of conjugated estrogens – so it’s really more than one hormone or drug.  The two main estrogens in Premarin are estrone and equilin. To see a more complete listing of estrogens in Premarin click here and scroll about half way down on this FDA document.

The first step in making a drug identical to the name brand is to know what’s in the brand name.  Guess what? It is not entirely clear what the exact makeup of Premarin is. Notice these words from the above referenced FDA document, “At least ten estrogenic compounds have been identified and quantified in Premarin”.  This suggests there are more estrogens not yet identified. If not all the compounds in Premarin have been identified then it is not possible for a pharmaceutical company that makes generic medications to prove that their generic compound is exactly the same as a the brand name Premarin tablets.

Keep in mind Premarin is the hormone that is most often used in studies accessing the safety and efficacy of hormone replacement therapy. in female patients. This is also the hormone that most women and physicians base their decision on to whether or not to receive or prescribe hormone replacement therapy – and it’s not entirely clear what is in Premarin. Premarin is frequently prescribed along with Provera, a synthetic progestin. Prempro is a combination tablet that contains both Premarin and Provera. Like Premarin, Provera is not a bioidentical hormone.

And That’s Why There is No Generic Premarin

Since it is not possible (at least at this time) for a drug manufacturer to show that its generic version of Premarin is exactly identical there is currently no generic Premarin on the market. That’s probably a blessing in disguise, though.  Premarin contains equine or horse estrogens that humans do not make, and some of those equine hormones are carcinogenic in humans. Though effective in treating symptoms of menopause as are bioidentical estrogen, Premarin is associated with side effects that are less likely to be expected from bioidentical hormones.

And, now you know the rest of the story. Now you know why there is no generic Premarin.

Article updated on 12/23/22.  Originally published on 5/26/13.