Abstract: The present disclosure provides methods of treating diseases, disorders, conditions, or syndromes, e.g., traumatic brain injury, in a patient in need thereof by administering a therapeutically effective amount of DL-leucine, or a pharmaceutically acceptable salt thereof, L-leucine, or a pharmaceutically acceptable salt thereof, D-leucine, or a pharmaceutically acceptable salt thereof, L-leucine ethyl ester, or a pharmaceutically acceptable salt thereof, acetyl-DL-leucine, or a pharmaceutically acceptable salt thereof, acetyl-D-leucine, or a pharmaceutically acceptable salt thereof, or acetyl-L-leucine, or a pharmaceutically acceptable salt thereof.