Inclusion Criteria1. Age >18 years old and < 80 years.
2. Diagnosis of primary ICH > 20 cc in volume.
3. Enrollment within 48 hours from initial symptoms.
4. Signed informed consent from the patient or obtained via their legally authorized representative (if the patient is not able to sign the informed consent themselves). The patient's decisional capacity to either provide or refuse consent will be determined using the Glasgow Coma Scale (GCS), which is being assessed at baseline and at 24 hours (+/-6hrs) after enrollment. A potential study participant with a GCS > 14 will be asked to provide their own initial study consent. A GCS ≤ 14 would indicate the need to pursue consent via legally authorized representative.
Exclusion Criteria1. Current need for renal replacement therapy (RRT).
2. Glomerular filtration rate (GFR) of <30 mL/minute at time of admission.
3. Participation in another study for ICH or intraventricular hemorrhage.
4. ICH related to infection, thrombolysis, subarachnoid hemorrhage, trauma or tumor.
5. Presence of HIV or active fungal infection that is known based on information in the electronic medical record (EMR).
6. Continued use of digoxin or amlodipine (as recommended by the manufacturer due to cytochrome P450 3A4 "CYP3A" inhibition).
7. Active hepatic failure as defined by aspartate aminotransferase (AST) >160 units/L and/or alanine transaminase (ALT) >180 units/L, or total bilirubin levels greater than four times normal levels (>4.8mg/dL).
8. Serum Na+> 145 mmol/L (admission labs or any time prior to recruitment/enrollment).
9. Unable to receive conivaptan based on contraindications indicated by the manufacturer.
10. Pregnant or lactating females.
11. Not expected to survive within 48 hours of admission, or a presumed diagnosis of brain death.