"Centrally acting" refers to substances or medications that exert their effects primarily on the central nervous system (CNS), which includes the brain and spinal cord. These agents can influence various physiological functions, such as pain perception, mood, and muscle control, by altering neurotransmitter activity within the CNS. Common examples of centrally acting medications include opioids for pain relief and antidepressants for mood disorders. These drugs can have significant effects on the body, often leading to side effects like drowsiness or changes in mental status, due to their direct action on the brain and spinal cord.