When switching from celexa to lexapro (escitalopram), (escitalopram) will the lexapro (escitalopram) still need to build up in my system before it starts to work or will it work almost right away?

It depends.: If you have already been on Celexa for several weeks, and your symptoms partially resolved or stabilized, then you will likely not have to wait a long time for Lexapro (escitalopram) to start working, as Celexa has already had time to start modulating the serotonin system in your brain. However, if you only took Celexa for a few days, then you will have to wait a full 2-4 wks to notice an effect.

Not necessarily: Depending how long were you on Celexa, Nevertheless time while on one SSRI usually counts when switching to another, if taken constantly, in your case Previous Celexa use should expedite or shorten Lexapro (escitalopram) effect to less then 3 weeks, but in pharmacotherary everything is individualy based Hope it helped MW

LEXAPRO (escitalopram): Yes it will still take some time to adjust to medication change. Lexapro (escitalopram) is the mirror image of celexa and tends to have less side effects. It may take 2-4 weeks. follow up with your doctor to adjust the dose as needed.