I was in one of the clinical trials for it. Even then they weren't trying to get it to be a stand-alone; the trial was to attempt to treat rapid cycling bipolar with a combination of lithium, depakote and lamictal. The combination was sort of ok for me but I never got to a therapeutic blood level of depakote in the 6 months of the study which made it less effective. My body eats up depakote for some reason and it wasn't until ER came out (right when I needed it) and we went to a really high dose that we could keep my levels where they belonged. By the time we had depakote working well I was off lamictal because it made me vomit every day about 10 AM. (I now kinda think that was birth control pills but it seemed like lamictal for some reason, probably because taking lamictal often made me vomit because there was a taste that I just couldn't handle but didn't have trouble with at all when I tried it again a few years later. Weird.)

Anyway, the role of the lamictal was supposed to be to tamp down depression, acting as an antidepressant without actually being one while depakote kept things level and lithium prevented mania.

Obviously that wasn't the plan for everyone on lamictal but it was a sign that they didn't intend for it to work alone in a lot of people.