ent S-(+)-Atomoxetine Hydrochloride is an enantiomer of Atomoxetine (Tomoxetine, LY 139603). This enantiomer is reported to be less effective than Tomoxetine as a competitive and specific inhibitor of norepinephrine reuptake. Tomoxetine (Atomoxetine, LY 139603) is a competitve and specific inhibitor of norepinephrine reuptake while demonstrating weak serotonin and dopamine inhibition as studied in synaptosomes of rat hypothalamus. Additional studies indicate that this (-) optical isomer is more effective than the (+) isomer, LY139602 (ent S-(+)-Atomoxetine Hydrochloride). Additionally, in the prefrontal cortex of rats, Tomoxetine was reported to not cause an increase in dopamine within the striatum or nucleus accumbens which may be useful in additional research studies investigating the reward pathways of the brain.