The purpose of this study is to determine whether metformin is effective in the treatment for sickle cell anemia (SCA).

This is a dose escalation, pilot study for subjects with sickle cell anemia (SCA) disease to determine if metformin has a beneficial effect on the treatment and quality of life of SCA patients.

Inclusion Criteria:

1. Confirmed diagnosis of sickle cell anemia
2. Age greater than or equal to 10 and less than or equal to 60 years of age.
3. If on hydroxyurea, fetal hemoglobin less than 20% at a stable dose (mg/kg) determined by the primary hematology provider over at least four months.
4. Creatinine less than or equal to 1.4 mg/dL and estimated glomerular filtration rate greater than 45 ml/min/1.73 m2
5. Liver function tests (specifically ALT and conjugated bilirubin) less than or equal to 4 times upper limits of normal.

Exclusion Criteria:

1. Failure to meet inclusion criteria
2. Simple or chronic red blood cell transfusion therapy in the last 3 months OR a HbA level greater than 5% in SCA patients
3. Refusal to use medically effective birth control if female and sexually active.
4. If on hydroxyurea, not at stable dose of hydroxyurea for a minimum of 4 months (temporary exclusion).
5. Creatinine greater than 1.4mg/dL
6. Liver function tests (ALT and conjugated bilirubin) greater than 4 times upper limits of normal.

The leftover blood samples for genetic analysis will be banked indefinitely for future ancillary studies. Investigator who desires access to these samples must present their research idea prior to receiving access to the samples. The samples will be shared with researchers affiliated with Texas Children's Hospital, Baylor College of Medicine and/or other hematology collaborators for future studies associated with hematologic diseases and drugs used to treat such diseases. The recipient investigators are required to provide proof of IRB approval or exemption as per local IRB guidelines before the sample can be released for research purposes. After receipt of IRB approval, coded samples will be distributed to the recipient investigator.