Fluoxetine is a selective serotonin reuptake inhibitor (SSRI) that works by blocking the reuptake of serotonin (5-HT) in the presynaptic neuron, which increases the levels of serotonin available in the synaptic cleft. This enhanced serotonin availability improves neurotransmission and helps regulate mood, anxiety, and other emotional responses. Fluoxetine has a high affinity for serotonin transporters with minimal effects on norepinephrine and dopamine systems. Its therapeutic effects usually appear after several weeks due to downstream receptor changes and increased brain-derived neurotrophic factor expression. It is widely used to treat depression, anxiety disorders, obsessive-compulsive disorder, and certain eating disorders.