GBT440 (previously GTx011) is a potent and direct drug for sickle cell treatment. In sickle cell anemia, abnormal hemoglobin molecules are formed, which causes problems for the flow of blood and oxygen through the body. GBT440 can selectively bind to hemoglobin, thereby increasing its affinity for oxygen. By inhibiting hemoglobin polymerization, it also prevents deformation of the red blood cells. GBT440, renamed Voxelotor, is thought to help prevent sickle cells blocking blood vessels, and therefore reduces pain (sickle cell crisis) experienced by patients. GBT440 is well absorbed following intravenous and oral administration, and quickly partitions into the red blood cell with a small part re‐distributed into the plasma. GBT440 was well tolerated in a randomized, placebo‐controlled, double blind, parallel group phase I/II study in healthy volunteers and sickle cell disease patients. Headache is the most reported adverse event related to the use of this drug, and no serious adverse events are known. A phase 3 clinical trial examining the efficacy and safety of the drug (compared to placebo) is planned to be completed in 2019. Voxelotor was also studied as a potential therapy for treatment of low oxygen levels in the blood of idiopathic pulmonary fibrosis patients, but this program was discontinued because of a lack of clinical benefits.