The purpose of this study is to evaluate the relative bioavailability of a single 300 mg dose of GBT440 administered as a high strength (1 × 300 mg) capsule versus a low strength (3 × 100 mg) capsule formulation in healthy fasted subjects.

Inclusion Criteria:

• Subject is a female of non-childbearing potential or male, who is healthy, nonsmoking, and 18 to 60 years old, inclusive, at screening
• Male subjects agree to use contraception
• Willing and able to give written informed consent

Exclusion Criteria:

• Evidence or history of clinically significant metabolic, allergic, dermatological, hepatic, renal,hematological, pulmonary, cardiovascular, gastrointestinal, neurological, or psychiatric disorder
• History of hypersensitivity or allergy to drugs, foods, or other substances
• History or presence of abnormal electrocardiogram or hypertension
• History of alcohol abuse, illicit drug use, significant mental illness, physical dependence to any opioid, or any history of drug abuse or addiction within 1 year of screening
• Participated in another clinical trial of an investigational drug within 30 days (or 5 half-lives of the investigational drug, whichever is longer) prior to Screening