What side effect is lithium associated with?

Lithium is primarily known for its use in the treatment of bipolar disorder and is associated with several side effects due to its impact on various systems in the body. One notable side effect of lithium therapy is hyperparathyroidism. This occurs because lithium can influence calcium metabolism and parathyroid hormone levels, potentially leading to an increase in parathyroid hormone secretion.

Hyperparathyroidism can manifest in various ways, including hypercalcemia (elevated calcium levels), which may result in symptoms such as fatigue, muscle weakness, and gastrointestinal disturbances. Chronic use of lithium has been linked to the development of primary hyperparathyroidism, especially in patients who have been on long-term treatment, making it a significant consideration in the management of patients receiving lithium. Monitoring serum calcium and parathyroid hormone levels in these patients is important for early detection of any disturbances.

The connection of lithium with other conditions mentioned, like neutropenia, pancreatitis, or eosinophilic colitis, is less direct or less prevalent among the patients treated with lithium. While these can occur in other contexts, they are not characteristic side effects of lithium therapy specifically, highlighting why hyperparathyroidism stands out as the most relevant answer.