900mg is not an awful lot of Lithium, it actually is used as a maintainance (sp?) level. My concern is the use of the Zoloft and that dosage. If you can have the pdoc try Lithobid instead of the Lithium carb., it may help. If you are a Bipolar-II, maybe Lamictal may be a better alternative, it has an
antidepresant property even though it isn't an AD, it is an antileptic drug but used as an antimanic for Bipolars, with mild manic episodes (hypomanic). Lithium (which I had been on) is fantastic for the agitation from manic episode or the approach of a manic episode, but doesn't quite do too much for depression. I had been on the Depakote/remeron/ celexa combo, dropped the depakote (nast stuff) opted for the Lithium and kept the celexa, celexa pooped out after so we switched to Lamictal, did great but with existing life problems I may be put on 3 tabs a day instead of the 2 that I presently take, no blodd tests required as in Depakote and Lithium use.
If I need in the future to return to Lihobid, I gladly will, it allowed me to still drive unlike the Depakote (zomby med) like anything you have to work and try different approachs, diferent combos till you feel most comfortable, like trying on new shoes till you find the most comfortable to walk the distance with.
Good luck to all
** hugs **

In giving advice seek to help, not please your friend
SOLON