Maybe this is a dumb question but I'm not really sure:

  Today I got my regular prescription re-filled and I'll be starting the new batch five days from now.  I've always been on the same brand of Estradiol, "Estrace," but this time the pharmacist said the formulary from my health plan provider had changed, so the pharmacy had to substitute a different brand that would still be covered by the insurance, "Lupin-Estradiol."  The tablets are nearly identical in appearance.

  If a particular brand says it contains "Estradiol" of a certain amount does that always mean it's exactly chemically identical?  How would I even be able to verify that?  Do I have to be concerned at all about reacting differently to it or the absorption rate being different?

I can't say for sure but it seems like price is the best indication. Estrace is one of many natural estradiol medications and because they are natural, they can't be patented. As the result, all the competition making the drug makes it pretty cheap. Because of my reduced dosage, I get 6 months worth for $20 but a transition dosage for 6 months could be as little as $40. Estradiol valerate breaks down to estradiol in the body but it's exclusive so the price would be higher.

As for a dumb question, I spend about a day trying to figure it out because nobody wants to tell you the truth that the next guys tablet is just as good as theirs.

theyre chemically identical. Its just a generic version of the exact same thing, and you have nothing to worry about. health plans want you to choose the generic version because it's cheaper!

  Okay, thanks!  It's just weird that the formulary covered Estrace for the nearly three years I've been taking it and only now part way through this year it changed.  I wasn't really expecting any noticeable differences since the pharmacy implied it's the same thing, but I will be paying close attention for a little while once I start on the new one.  I'm seeing my doctor again in a little over a week for an unrelated issue so I'll ask her about that anyway.

According to my wife, the chemist of the family, as in she once blew herself up.... not all compounds are created equally. Though the compound is said to be this big long bunch of letters and numbers, how you get from from a bunch of much smaller or larger bunches of letters and numbers to the final end product changes. All the ingredients and the various processing steps along the way never produce 100% pure (on paper) results. These steps and process are even more proprietary then the actual chemical. As in a trade secret. Not all generics are created equal.

I do injectable EV. When I first started it was some off-shore brand and worked as far as I could tell. In time I started getting a USA manufactured brand and wow what a difference. Almost like my first ever shot.

My wife suffers from chronic pain from a childhood injury. (unrelated to blowing herself up but close) She has been taking percoset for ages. Our 'Local' independant pharmacy seems to have a different supplier every month. For years it would be the pills are working OK, or they don't help at all. Since another script I filled her was at a chain I did the percoset there also. Those worked great. Next month, same brand. Month after that same again. Same for a year now. Much the same with her Fentynil patches. The squishy ones work, the paper tape ones don't no matter who makes the paper tape ones. So we use the pharmacy that gets the squishy ones for that