Lamotrigine therapy usually starts at 25mg daily for 14 days, increasing to 50mg daily for another 14 days. It can then be increased to a max of 50-100mg daily every 7-14 days. Maintainence as monotherapy can be 100-200mg daily in divided doses (i.e. twice daily). It has been known that up to 500mg daily has been required.
Whatever you do, don't suddenly stop taking Lamotrigine, and keep an eye out for side effects, as described in the medication leaflet. They are rare though.
Hope this helps.