Lexapro is the "next generation version" of Celexa , according to Forest Pharmaceuticals, the manufacturers of both medication brands.

In actuality, the two medications are almost the same chemically, except that Lexapro excludes one of the two isomers ( enantiomer to be more exact) which compose Celexa.

Citalopram hydrobromide ( the chemical name for Celexa ) is comprised of two enantiomers (R-enantiomer and S-enantiomer) .The dictionary definition of enantiomer is:

Either of two stereoisomers that are mirror images of one another but cannot be superimposed on one another and that rotate the plane of polarized light in opposite directions. Enantiomers usually behave the same chemically but differ in optical behavior and sometimes in how quickly they react with other enantiomers. Also called optical isomer, enantiomorph.

The compounds which differ from one another only in the way the atoms are oriented in space and are nonsuperimposable mirror-images of one another. Many compounds used as medications are comprised of enantiomers.

Celexa has two enantiomers, the R-enantiomer and the S-enantiomer. Wow, that explains a lot, doesn't it. To make Lexapro,

Ahh, so Lexapro is the better half of Celexa. The S-enantiomer is apparently the only one of those two enantiomers which has antidepressant qualities, and by extracting it from Celexa, a concentrated or more potent form, we get Lexapro. Interestingly, Forest Labs, in one of its press releases (see below), claims that Lexapro has more than twice the potency of Celexa.