Used primarily in the treatment of vitamin D deficiency and related disorders such as osteoporosis and secondary hyperparathyroidism, especially in patients with impaired kidney function who cannot effectively convert vitamin D to its active form. It serves as a direct replacement therapy because it is the biologically active metabolite of vitamin D3. Commonly prescribed for individuals with chronic kidney disease, malabsorption syndromes, or those on medications that interfere with vitamin D metabolism. Also used to support bone health and calcium absorption in elderly patients and in managing certain metabolic bone diseases. Its use allows for more predictable serum levels of active vitamin D compared to standard vitamin D supplements.