Actigraphy Improvement With Voxelotor (ActIVe) Study (ActIVe)

Inclusion Criteria:

1. Male or female participants with SCA (sickle hemoglobin with two sickle cell genes [HbSS] or sickle hemoglobin (S) and one beta thalassemia gene [HbS β0] thal genotype)
2. Between 12 to 55 years of age (inclusive)
3. Screening Hb level ≤8.0 g/dL
4. Treatment with hydroxyurea (HU) therapy on study is permitted if the participant has been on a stable dose for at least 90 days before enrollment with no dose modifications planned or anticipated by the Investigator
5. Treatment with glutamine is permitted
6. Treatment with erythropoiesis-stimulating agents (ESAs) is permitted if the participant has been on a stable dose for at least 12 weeks before enrollment with no dose modifications planned or anticipated by the Investigator
7. Female participants of child-bearing potential must use highly effective methods of contraception to 30 days after the last dose of study drug. Male participants must use barrier methods of contraception to 30 days after the last dose of study drug
8. Females of child-bearing potential are required to have a negative pregnancy test before the administration of study drug
9. Written informed consent and/or parental/guardian consent and participant assent per Institutional Review Board (IRB) policy and requirements, consistent with ICH guidelines

Exclusion Criteria:

1. Red blood cell (RBC transfusion within 3 months before initiation of study drug
2. Planned initiation of regularly scheduled RBC transfusion therapy (also termed chronic, prophylactic, or preventive transfusion) during the study
3. Hospitalization for vaso-occlusive crisis (VOC) or acute chest syndrome (ACS) within 30 days prior to informed consent/assent.
4. More than 10 VOCs requiring hospitalization, emergency department or clinic visit within the past 12 months
5. Planned elective surgery within the next 6 months
6. Physical inactivity attributable to clinically significant musculoskeletal, cardiovascular, or respiratory comorbidities
7. Anemia due to bone marrow failure (eg, myelodysplasia)
8. Absolute reticulocyte count (ARC) < 100 x10^9/L
9. Screening alanine aminotransferase (ALT) > 4× upper limit of normal (ULN)
10. Severe renal dysfunction (estimated glomerular filtration rate [GFR] < 30 mL/min/1.73 m2 by Schwartz formula) or is on chronic dialysis
11. Known active hepatitis A, B or C or known to be human immunodeficiency virus (HIV)-positive.
12. Females who are breast-feeding or pregnant
13. Major surgery within 8 weeks before enrollment. Participants must have completely recovered from any previous surgery before enrollment
14. History of hematopoietic stem cell transplant or gene therapy
15. Received an investigational drug within 30 days or 5-half-lives, whichever is longer, prior to consent, or is currently participating in another trial of an investigational or marketed drug (or medical device)
16. Use of concomitant medications (eg, crizanlizumab) that confound the ability to interpret data from the study
17. Medical, psychological, or behavioral condition that, in the opinion of the Investigator, would confound or interfere with evaluation of safety and/or efficacy of the study drug, prevent compliance with the study protocol; preclude informed consent; or, render the participant unable/unlikely to comply with the study procedures
18. Use of herbal medications (e.g., St. John's Wort), sensitive cytochrome P450 (CYP) 3A4 substrates with a narrow therapeutic index, strong CYP3A4 inhibitors, fluconazole, or moderate or strong CYP3A4 inducers
19. Symptomatic coronavirus disease of 2019 (COVID-19) infection