A single psilocybin injection given a full year after traumatic brain injury reversed motor deficits and memory impairment in rats, restored depleted serotonin receptors (p = 0.001), and reduced the brain's chronic inflammation response — in a condition that currently has zero approved treatments. The drug only triggered these changes in injured brains, not healthy ones, suggesting it targets damage specifically rather than altering normal brain chemistry. With ~70 million TBIs happening annually and survivors often stuck with permanent deficits long after recovery plateaus, a single dose that reverses both receptor damage and neuroinflammation a year later puts psilocybin on the map as the first real pharmacological candidate for chronic TBI.