The chemical modification of the morphine molecule to hydromorphone results in higher lipid solubility and greater ability to cross the blood-brain barrier to produce more rapid and complete central nervous system penetration. On a per milligram basis, hydromorphone is considered to be five times as potent as morphine; although the conversion ratio may vary from 4-8 times, five times is in typical clinical usage.

Patients with renal abnormalities must exercise caution when dosing hydromorphone.