Efficacy and effectiveness of hydroxyurea for children with sickle cell disease (SCD), based primarily on observational studies. Adapted from Strouse et al.17
| Outcome | Number of studies | Effect | Evidence grade |
| %HbF | 17 | Increased | High |
| Hemoglobin | 16 | Increased | High |
| Pain episodes | 5 | Decreased | Moderate |
| Hospitalization | 5 | Decreased | High |
| Transfusions | 3 | Decreased | Insufficient |
| Neurological events | 3 | Decreased | Low |
| Splenic function | 3 | Improved | Low |
| Outcome | Number of studies | Effect | Evidence grade |
| %HbF | 17 | Increased | High |
| Hemoglobin | 16 | Increased | High |
| Pain episodes | 5 | Decreased | Moderate |
| Hospitalization | 5 | Decreased | High |
| Transfusions | 3 | Decreased | Insufficient |
| Neurological events | 3 | Decreased | Low |
| Splenic function | 3 | Improved | Low |