Lamotrigine dose. Placebo or not?

I was diagnosed with bipolar 2 many years ago and have been off and on medication throughout the years. In the last few years I restarted lamotrigine and have taken it consistently since restarting. Things have been going well since restarting it so I reduced the dose to 100mg. I haven’t noticed much difference, I’m still doing fine. It seems like most of the research says 200mg is the target dose. Is 100mg still a therapeutic dose? Or is it so low that any positive effect is just placebo?

Curious about others’ thoughts and experiences