The relationship between serotonin transporter occupancy and extracellular serotonin concentration is hyperbolic, not linear: implications for safely tapering antidepressants

The research examines the theoretical basis of hyperbolic tapering of serotonin reuptake inhibitor (SRI) antidepressants. Scientists developed a mathematical model based on mass-action kinetics to evaluate the relationship between serotonin transporter (SERT) occupancy and extracellular serotonin concentration during chronic SRI treatment. The analysis shows that serotonin concentration increases hyperbolically with increasing transporter occupancy. Although SERT occupancy plateaus within the therapeutic dose range of SRIs, the model predicts that biologically meaningful differences in serotonergic signaling persist within this range. The results suggest that changes in transporter occupancy may not proportionally translate into biological effects. These findings provide a potential explanation for dose-dependent clinical effects of SRIs and generate testable hypotheses regarding antidepressant tapering strategies.