The search for effective Alzheimer's treatments may have found an unexpected ally in lithium, a mood stabilizer that's been used in psychiatry for decades. This development could represent a significant shift from expensive, hard-to-access antibody therapies toward a widely available, affordable medication already proven safe for long-term use. Recent pilot clinical trial data suggests lithium may slow cognitive decline in people with mild cognitive impairment, the precursor stage to Alzheimer's dementia. The mechanism appears to involve lithium's ability to inhibit GSK-3β, an enzyme that promotes tau protein aggregation—one of the hallmark pathological features of Alzheimer's disease. Additionally, lithium enhances autophagy, the cellular cleanup process that removes damaged proteins and organelles. The clinical evidence builds on decades of observational studies showing lower dementia rates in populations with higher natural lithium exposure through drinking water. Danish registry data revealed a dose-dependent relationship: areas with moderate lithium levels in water supplies showed reduced Alzheimer's incidence compared to low-lithium regions. However, the therapeutic window appears narrow—very high concentrations may actually increase risk. The pilot trial's positive signals are encouraging, but significant limitations remain. The study was small and short-term, and lithium requires careful monitoring due to potential kidney and thyroid effects. Unlike the recent FDA-approved amyloid-targeting drugs that cost tens of thousands annually, lithium costs mere dollars per month. If larger Phase 3 trials confirm efficacy, this could democratize Alzheimer's prevention and early treatment globally. The approach represents a promising example of drug repurposing, where existing medications find new therapeutic applications through better understanding of disease mechanisms.