FURTHER to the reference of generics in the “Alternatives To Conjugated Equine Estrogens” report, I think a separate word on the availability of generic Premarin® and its daughter drugs is warranted to clear up any confusion for those seeking to avoid products manufactured from the urine of pregnant mares.
Premarin has a long and interesting history when it comes to FDA approval of generics, a history mired in the ruthless and bloodthirsty battle of Big Pharma patent wars.
Many years ago, in 1986, the effectiveness of Premarin’s®, and other short-term acting estrogens, ability to diminish bone loss associated with osteoporosis was granted approval by the FDA. What was once a drug that was prescribed for the relief of menopausal symptoms now became the panacea for a long-term chronic problem.  And with this came a huge untapped market.
At this time there were certified generics that were interchangeable with Premarin®. However because of the ramifications of long-term use, the science behind the drugs prevailed.
While Premarin® provided slow-release bioavailability, the generics were immediate release. This disparity in mode of release would turn into a long battle between the generic manufacturers, Wyeth-Ayerst and the FDA. 
To make a long story short, the outcome of detailed analysis showed that the bioavailability of generic versions was not equivalent to Premarin® and in 1991 the FDA withdrew approval of all ANDAs (Abbreviated New Drug Applications) proclaiming that none of the synthetics on the market could be considered generic versions of Premarin®. 
Because of the lucrative market potential, two generic manufacturers – Duramed and Barr – set out to develop products that solved the bioavailability problem and submitted ANDAs for FDA approval. Both met the requirements of adsorption efficiency however Wyeth had been conducting its own research and contested FDA approval on the grounds that the generic drug lacked one of the estrogens, called delta 8,9 (dehydroestrone sulfate), present in Premarin®. Nevertheless, in 1994, the FDA unanimously ruled that delta 8,9 (dehydroestrone sulfate) was an impurity and not a required ingredient of a generic version.
Duramed applied for FDA approval of Cenestin in September 1995, and Barr followed the next July. 
What happened next effectively blocked any competitor from manufacturing a generic Premarin®. Propaganda and political persuasion tactics were used to coerce the FDA and in 1995 Wyeth-Ayerst successfully petitioned the FDA to require the presence of delta 8,9-dehydroestrone in any generic version of Premarin®.  Together with Wyeth-Ayerst’s patent on synthetic delta 8,9-dehydroestrone, this shut out the competitors.
Eventually Duramed filed a NDA (New Drug Application) for its synthetically derived estrogen Compound Cenestin which is still available on the market today along with a variety of other synthetic products, none of which contain pregnant mare’s urine.
Premarin® lost its patent in February 2012 and the patent for Prempro® held by Wyeth Pharmaceuticals, does not expire until early 2015.
Despite Premarin’s® patent expiration there seems to be no interest in manufacturing a generic version from pregnant mare’s urine.  In any case, it would be challenging for another pharmaceutical company to synthesize a medication that is similar enough to Premarin® to receive the approval of the FDA, similarly so for Prempro® as it contains the same natural conjugated equine estrogens as Premarin®.
The so-called Premarin generics are the lab-synthesized versions manufactured from plant sources not pregnant mare’s urine (see “Alternatives to Drugs Made with pregnant Mare’s urine). 
As a reminder, these drugs carry with the same serious risks as the Premarin® family of drugs.
Some will say that generic Premarin® is available online without prescription, particularly from Canada. However be wary of any medications that tout themselves as being a safe generic version of Premarin®. Congressional testimony from the US FDA points out the dangers of inadequately regulated foreign Internet sites which have also become portals for unsafe and illegal drugs. This excerpt specifically targets Canadian generic websites. 
“A recent example illustrates some of the dangers associated with the purchase of prescription drugs from rogue pharmacy sites. Within the last six months, FDA has examined two web sites having identical web pages headlined "Canadian Generics" which were identified through spam e-mails sent to consumers. FDA has purchased prescription drugs from both of these sites, and has found that these drugs and the manner in which they are sold pose potential threats to the health and safety of consumers.
There is at least one Canadian flag on every page of these sites, as well as the words "Canadian Generics." The web sites say, "Order Canadian to get the biggest discounts!" Both of the URLs from which the orders were placed suggest the sites are located in, and operated out of, Canada. Despite these representations, however, we determined there is no evidence that the dispensers of the drugs or the drugs themselves are Canadian. The registrants, technical contacts, and billing contacts for both web sites have addresses in China.”
There is currently no therapeutically equivalent version of Premarin® available in the United States. In other words, there is no approved generic for Premarin in the US.
The drug policies and generic approval practices in other countries may vary. What is a generic in one country may not be approved as one in another.
Fraudulent online pharmacies may attempt to sell an illegal generic version of Premarin®. These medications may be counterfeit and potentially unsafe.
If you purchase medications online, be sure you are buying from a reputable and valid online pharmacy. 
Always consult your doctor before embarking on any change in medication
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Last Updated March 9, 2015