Doseage is everything. The starting dose of Celexa is usually 20mg, the high dose is probably 40mg. Lexapro is the improved version, exactly twice as potent (for complicated chemical reasons). Some people report an immediate calming effect of taking a higher dose, this is probably more of a side effect instead of a therapeutic effect of the antidepressant action as that generally takes another 2-4 weeks to develop when increasing dose from a lower dose. Celexa is now generic I believe as well.