What condition can result from prolonged use of Lithium?

Prolonged use of lithium, a medication commonly used for the management of bipolar disorder, can lead to hypothyroidism. This condition occurs when the thyroid gland does not produce enough thyroid hormone, which is crucial for regulating metabolism, energy levels, and overall bodily function. Research indicates that lithium can interfere with thyroid function, often leading to a decrease in hormone production over time. Clinicians monitor thyroid levels in patients on lithium to ensure any symptoms of hypothyroidism, such as fatigue, weight gain, and depression, can be addressed promptly.

The other conditions presented are not typically associated with long-term lithium use. For instance, hypertension and diabetes mellitus are not direct side effects of lithium, while hyperthyroidism, which is characterized by excessive thyroid hormone production, is not something that lithium is known to induce. Therefore, hypothyroidism is the most relevant and well-documented condition that may arise from the extended use of lithium.