Just went from 20 mg of cymbalta (duloxetine) to 40 mg. how long until a therapeutic level would be noticed?

About 6 Weeks.: Although the claim is made that some people may be able to start to feel less depressed within 2 weeks of taking one of these kinds of antidepressants, most people won’t start experiencing the full positive effects of the medication until 6 to 8 weeks after beginning it. It alters brain chemistry so it takes longer to get to those effects.