Described are methods and compositions for treating subjects for symptoms from unplanned radiation or protecting subjects therefrom. Embodiments include methods of treating subjects exposed to unplanned radiation with pharmaceutical compositions comprising a biguanide compound. In further embodiments, methods and compositions are provided for radioprotection by administering pharmaceutical compositions comprising a biguanide compound and additional therapeutic compounds.
 The invention was made with government support under Grant No. R01-CA132998 awarded by the National Institutes of Health and Grant No. DE-SC0001271 awarded by the Department of Energy. The government has certain rights in the invention.