Metformin has been shown to help prevent weight gain in patients who take neuroleptic mood stabilizers.
Lamotrigine (aka Lamictal) can be a great option for many; here are some indications and some things to watch for.
Oxcarbazepine is sometimes used to treat bipolar disorder and symptoms related to mood dysregulation.
Ketamine for bipolar depression is thought to be safe as long as the patient is also on a mood stabilizer.