Cutting the dose in half was the recomendation of my doctor and pharmacist. The first month I was on the meds I forgot to cut it in half and had a very manic week. This week has been much better and I have managed to control the manic episodes while only taking half dose. Cannot remember all the details but this is what I found online

" For women not taking carbamazepine, phenytoin, phenobarbital, primidone or rifampin, the maintenance dose of lamotrigine will in most cases need to be decreased by as much as 50%, in order to maintain a consistent lamotrigine plasma level"

Found it on the mims website but I am unable to post the link as I am new and do not have permission to post links.