Long-term lithium carbonate therapy causes hyperparathyroidism.

Twelve patients taking lithium carbonate for two to 13 years were compared with age- and sex-matched controls to determine whether long-term lithium carbonate therapy is associated with alterations in calcium metabolism. As a group and individually, patients had significantly higher levels of serum total calcium, ionized calcium, and parathyroid hormone. When compared with serum calcium levels, patients' parathyroid hormone levels were significantly more likely than those of controls to indicate hyperparathyroidism. Lithium carbonate-induced mild hyperparathyroidism appears to be more common than had previously been suspected.