There is a psychologist who went to UCLA with my pdoc (She now teaches at John Hopkins University). She has written several books on Bi-polar and co-authored a text book with a pdoc. She has Bi-polar and also complained about not having her highs and having a little breakthrough depression. She asked her pdoc if she could reduce her lithium by one each day until she felt better. He OK'd it and she stated she could not believe the difference in the color of a rose by the decrease in her meds.
I take lithium and when I have breakthrough depression (especially in the Spring or from a trigger, my pdoc prescribes my lithium in 150mg doses and 300mg doses in case I do need to take a little less (900mg one day, 750mg the next and alternate until I feel a little more than hypomanic and then return to therapeutic level.)