Off-label use of the malaria drug quinine sulfate to treat leg cramps has caused serious adverse events in some patients, including bleeding disorders, permanent kidney damage, and death, warns the US Food and Drug Administration (http://www.fda.gov/Safety/MedWatch/SafetyInformation/SafetyAlertsforHumanMedicalProducts/ucm218424.htm).
Kuehn BM. Quinine Sulfate Warning. JAMA. 2010;304(8):846. doi:10.1001/jama.2010.1197