Consolidated Standards of Reporting Trials flowchart. *Informed consent/assent received. ^†The most common reasons for exclusion were: absent or inadequate/incomplete transcranial Doppler imaging (n = 23), abnormal liver function test results (n = 20), hemoglobin <6 g/dL (n = 18), judged unsuitable by the principal investigator (n = 12), and not having experienced at least 2 vaso-occlusive crises in the past 12 months before visit 1 (n = 12). ^‡Randomized to double-blind study treatment and received at least 1 dose of double-blind, randomized study treatment. ^§Includes patients who prematurely discontinued study treatment. ^¶Lost to follow-up: patients were only considered lost to follow-up after 3 documented failed attempts to reach the patient, and all other options of reaching the patient had been exhausted.