Used as an active metabolite of mycophenolate mofetil in immunosuppressive therapy, particularly in organ transplant recipients to prevent rejection. It selectively inhibits inosine monophosphate dehydrogenase, blocking purine synthesis in lymphocytes, thereby suppressing T and B cell proliferation. Its role is critical in maintaining long-term graft function when combined with other immunosuppressants like cyclosporine and corticosteroids. Monitoring levels of this compound helps optimize dosing and reduce toxicity in patients.