A normal lithium level falls between 0.6 millimoles per liter and 1.2 millimoles per liter for people who are taking the drug. This is also known as the therapeutic range, according to Lab Tests Online.
The lithium level is monitored when a person is taking lithium in order to make sure that the level remains within an acceptable range. This is called therapeutic drug monitoring. If the person responds to the drug without showing signs of toxicity, then the lithium is likely within the normal range. Blood is drawn 12 hours after the last dose for this test.
Symptoms of lithium toxicity include dizziness, drowsiness, slurred speech, nausea, vomiting, diarrhea, confusion, muscle weakness, and shaking or tremors. At extreme levels, lithium toxicity sometimes causes kidney failure or death, according to Lab Tests Online.