Hydoxyurea Exposure in Lactation A Pharmacokinetics Study (HELPS)

Inclusion Criteria: * Lactating females, ≥ 18.0 years of age, at the time of enrollment * Willingness to limit the baby's exposure to hydroxyurea through breastmilk, such as healthy volunteers using the "pump and dump" technique or avoiding direct breastfeeding or collection of pumped milk for at least 8 hours after taking the hydroxyurea dose. This applies only to healthy controls or women with sickle cell who are not already taking hydroxyurea. Women with sickle cell already taking hydroxyurea may continue to breastfeed their infants. Exclusion Criteria: * Persons with known allergies to hydroxyurea * Failure to sign informed consent, or inability to undergo informed consent process * Persons for whom it is not feasible or medically advisable to obtain the specimens necessary for this study