Mirtazapine
"Normally antidepressants work on me within a few days to a week if they are going to work at all. Not so with mirtazapine! It took about 4 weeks to work and when it did, it improved my depression and anxiety symptoms more than any other antidepression/antianxiety drug I have ever taken (Lexapro, Wellbutrin, Cymbalta, Effexor, Klonopin). I am glad I didn't give up on it after a short time, for I never would have discovered how well it worked for me!"