Lithium toxicity (too much lithium in your body) can cause death. Lithium toxicity can occur if you take only slightly more than a recommended dose.
Stop using lithium and call your doctor right away if you have symptoms of lithium toxicity: muscle weakness, twitching, drowsiness, feeling light-headed, mood changes, blurred vision, ringing in your ears, irregular heartbeats, confusion, slurred speech, clumsiness, trouble breathing, or seizures.