from "alkali springs" as a treatment. Although they were not aware of it, they were actually prescribing lithium, which was present in high concentration within the waters. The therapeutic effect of lithium salts appears to be entirely due to the lithium ion, Li+. Its exact mechanism of action is uncertain, although there are several possibilities such as inhibition of inositol monophosphatase, modulation of G proteins or regulation of gene expression for growth factors and neuronal plasticity. There is strong evidence for its effectiveness in acute treatment and prevention of recurrence of mania. It can also be effective in bipolar depression, although the evidence is not as strong. It is also effective in reducing the risk of suicide in patients with mood disorders. Potential side effects from lithium include gastrointestinal upset, tremor, sedation, excessive thirst, frequent urination, cognitive problems, impaired motor coordination, hair loss, and acne. Excessive levels of lithium can be harmful to the kidneys, and increase the risk of side effects in general. As a result, kidney function and blood levels of lithium are monitored in patients being treated with lithium. Therapeutic plasma levels of lithium range from 0.5 to 1.5 mEq/L, with levels of 0.8 or higher being desirable in acute mania. Lithium levels should be above 0.6 mEq/L to reduce both manic and depressive episodes in patients. A recent review concludes that the standard lithium serum level should be 0.60-0.80 mmol/L with optional reduction to 0.40-0.60 mmol/L in case of good response but poor tolerance or an increase to 0.80-1.00 mmol/L in case of insufficient response and good tolerance. Monitoring is generally more frequent when lithium is being initiated, and the frequency can be decreased once a patient is stabilized on a given dose. Thyroid hormones should also be monitored periodically, as lithium can increase the risk of hypothyroidism. Anticonvulsants A number of anti-convulsant drugs are used as mood stabilizers, and the suspected mechanism is related to the theory that mania can "kindle" further mania, similar to the kindling model of seizures. Valproic acid, or valproate, was one of the first anti-convulsants tested for use in bipolar disorder. It has proven to be effective for treating acute mania. The mania prevention and antidepressant effects of valproic acid have not been well demonstrated. Valproic acid is less effective than lithium at preventing and treating depressive episodes. Carbamazepine was the first anti-convulsant shown to be effective for treating bipolar