Usually for bipolar disorder antidepressants are used in conjunction with mood stabilizers (Lithium, Depakote, Lamictal to name a few). WHat can happen (I know from experience) is taking an antidepressant alone can throw you into a hypomanic or manic episode. Clearly that's not desirable. You didn't say whether or not you were on any mood stabilizer with the Cymbalta but it's definitely worth asking him again to be sure he feels there would be no complications from an antidepressant alone. Good luck and hopefully it works well.