Hello and thanks for your question on JustAnswer. I'm DrMike, a pharmacist with over 20 years experience, and I'm glad to help you today!
As you likely know, Lexapro (escitalopram) is an SSRI (Selective Serotonin Reuptake Inhibitor) which works to increase the hormone/neurotransmitter Serotonin in your system. A decrease in serotonin has been associated with effects on mood, diposition, anxiety (and many other things)
All SSRI's take generally 4-6 weeks to 'kick in'. I have reviewed the scientific literature on Lexapro specifically and all studies showed benefit over taking nothing (or placebo). Most studies lasted up to 8 weeks (2 mo's), but there has been suggestion that maximal benefit can take up to 36 weeks (9 mo's).
Dose increases (from say, 10 to 20mg) may occur as early as 1 week after beginning therapy if determined necessary, but studies do not show a substantial benefit of the higher 20mg dose.
I believe this addresses your concern, but if you would like further clarification, let me know.
If you are satisfied, please do Accept and Rate my response so that I might evaluate and improve upon my assistance!
I wish you all the best -DrMike