Prescription medications affect the brain by altering neurotransmitters—chemicals that regulate mood, pain, attention, and sleep. For example, antidepressants adjust serotonin, stimulants influence dopamine, and sedatives like Diazepam enhance calming signals. When used properly, they restore balance and improve symptoms. Misuse or long-term overuse can disrupt brain function, leading to dependence, tolerance, or cognitive changes. Effects vary widely depending on the drug class, dose, and individual biology.