Lithium used in the treatment of bipolar disorder is administered as a salt. Therefore, plasma concentrations of lithium are dependent on salt balance. Excess sodium intake promotes additional renal excretion of salt, leading to eradication of serum lithium and resulting in non-therapeutic lithium levels. Because therapeutic levels of lithium are close to toxic levels, it is most important to stress balanced dietary salt intake (~5-6 g/day). If dietary salt intake is decreased or eliminated, then lithium levels can rise, leading to toxicity. Conversely, if dietary salt intake is increased, then lithium levels may drop to sub-therapeutic levels.