This study is about osivelotor, a medication being tested for people with sickle cell disease (SCD). SCD is a condition where red blood cells are shaped like a sickle, making it hard for them to move through blood vessels and carry oxygen. The study has three parts. In Part A, researchers check the safety and how well osivelotor works in adults. Part B compares the effects of osivelotor and a placebo (a pill with no medicine in it) in adults and teenagers over 48 weeks. An Open Label Extension (OLE) looks at the long-term effects of osivelotor for those who finish Part B.

Key Points:

• The study lasts for 48 weeks in Part B, plus an OLE for long-term observation.
• Participants need to visit the study center regularly for check-ups and monitoring.
• Participants may not be able to join if they have frequent hospital visits or other health issues.