Potent, high affinity serotonin re-uptake inhibitor; selective in vivo. Displays moderate selectivity over noradrenalin and dopamine re-uptake in vitro (Ki values are 0.68, 2.9 and 36.8 nM for inhibition of serotonin, noradrenalin and dopamine uptake respectively in rat brain synaptosomes). Potently potentiates 5-HT-induced effects in vivo following oral administration. Biological activity resides predominantly in the (+)-enantiomer.