For me, a decrease in Lamictal could mean increased depression. I know it affects others differently. I actually regard my Lamictal as my "antidepressant" that is activating for me. My Seroquel XR contributes for both ends of the spectrum, depending on my dose and current situation.

I hope that if your psychiatrist recommends a small reduction in your Lamictal that you perhaps give that a try for at least a bit to see what happens. The reduction you're interested in seems like a huge one, indeed. I don't have anything against doses of 100 mg, though. I've taken 100 mg for almost 8 years now. I have been on doses of Lamictal up to 300 mg long ago in the past, and became severely manic w/psychosis on that dose (along with Abilify). I do appreciate my 100 mg of Lamictal, because it was that dose/med that pulled me out of a long depression (I was also on Lithium and Geodon at the time), but when I reached the 100 mg, I was getting very hypomanic. My doctor had to add a second antipsychotic to offset that. He chose not to increase the Lamictal since it was clearly activating for me, and had a history of being more so at the higher doses. Instead, he manipulates my Seroquel XR dose, usually up or down by 50 mg, unless I get more manic, at which time he increases it by 150 or 200 mg or so. Then when my mania eases, he lowers it again, but by small amounts.