low doses working?

[dancesintherain]

I'm mostly asking because I'm curious--not because I'm tempted to upend the apple cart.  I'm currently taking three typical BP drugs (I've been psychotic, manic, and depressed within the past two years) but at rather low doses.  The lithium is at 600mg with a blood level of around 0.55/0.6 (in part because one of my most recent hospitalizations I was toxic).  The lamictal's at 200mg (I think that's normal).  The zyprexa is only at 7.5mg.  My current (new-ish to me) psychiatrist had initially been surprised at three meds that have somewhat overlapping significance at low levels, but it's what I left the hospital on and it seems to be doing okay, so we haven't changed it.  Initially the hospital brought me down to the 600mg lithium once I was detoxed and kept me on the zyprexa at the lower dose.  But I was still showing signs of depression and I had better luck with lamictal than with SSRIs/SNRIs.

I'm curious whether there's an explanation for why this approach might work.  I've been quite sensitive to some meds (I've gotten about every variation of EPS that exists, cogentin caused blurred vision, ambien caused sleep-walking, eating, and arguing).  So maybe it's preventing that problem?  I also know the most recent two hospitalizations were largely med-related because once they were changed, my suicidal ideation vanished...it wasn't a progressive relief, it was close to instantaneous.  Which isn't typical for me.