USMLE (United States Medical Licensing Examination) Step 1 Practice Exam 2025 - Free USMLE Step 1 Practice Questions and Study Guide

Thiazide diuretics are primarily known for their ability to promote diuresis by inhibiting sodium reabsorption in the distal convoluted tubule of the nephron. One of the well-recognized side effects associated with thiazide therapy is hypercalcemia, meaning increased calcium levels in the blood.

Thiazides can increase calcium reabsorption in the renal tubules, which often leads to elevated serum calcium concentrations. This property can be therapeutically beneficial in certain conditions like kidney stones or osteoporosis, but it is noteworthy because prolonged hypercalcemia may have detrimental effects.

Other common side effects of thiazide diuretics include mild elevations in blood sugar levels due to changes in glucose metabolism, as well as a risk of hypokalemia instead of hyperkalemia since thiazides can cause potassium loss in the urine. While they can cause acute kidney injury under certain conditions, such as dehydration or in susceptible patients, this is less common compared to the more frequently observed effects such as hypercalcemia.

Therefore, the understanding of thiazide diuretics includes that their mechanism not only affects fluid balance but can also influence electrolyte levels, particularly calcium, leading to the notable side effect of increased serum calcium levels.