What is the need of llamotrigine for a patient who is having lithuim?

Lamotrigine: Lamotrigine is an anticonvulsant that's also sometimes used to stabilize mood in bipolar disorder. People may have both seizure disorder and bipolar disorder. Lithium can be very helpful for bipolar disorder -- but if it isn't controlling moodswings at therapeutic doses, the doctor may add another medication (lamotrigine). Also one may be in process of changing from lithium to lamotrigine.

Lamictal: The patient may be transitioning from one mood stabilizer to another or a second mood stabilzer might be added due to inadequate response from the first one.