Actually, lamotrigine, carbemazepine, and valproic acid are all approved by the FDA as monotherapy for BP I. Things like topiramate (brand Topamax) and
oxcarbazepine (brand Trileptal) are off-label, but the anticonvulsants in general are known for mood stabilization properties (oxcarbazepine is very similar to carbemazepine, but with fewer side effects, and a lack of license might be a monetary thing, not a clinical one).