LY-393558 is a potent serotonin reuptake inhibitor and antagonist of the 5-HT<sub>1B</sub>, 5-HT<sub>1D</sub>, and 5-HT<sub>2A</sub> receptors. LY-393558 was also found to reduce serotonin-induced vasoconstriction, indicating that it may have therapeutic potential for the treatment of pulmonary hypertension.