Not recommended. If you're intent on stopping, drop the lithium to 900 mg for one week, then 600 mg for one week, then 300 mg for two weeks, then stop. You need to tamper this drug, if you don't you could trigger a relapse. Furthermore, you might find that taking a lower dose is tolerable. Any amount of lithium in your system is better than no lithium.

I would not discontinue both drugs at the same time.