<b><i>Background/Aims:</i></b> Attention deficit hyperactivity disorder (ADHD) is frequently associated with other psychiatric pathologies. Therefore, the present study investigated a possible pharmacokinetic interaction between atomoxetine (ATX), a treatment option for ADHD, and an antidepressant, namely, fluvoxamine (FVX). <b><i>Methods:</i></b> Designed as an open-label, non-randomized clinical trial, the study included 2 periods. In period 1 (reference), each subject received ATX 25 mg (single-dose), whereas in period 2 (test), all subjects were given a combination of ATX 25 mg + FVX 100 mg, following a 6-day pretreatment regimen with the enzymatic inhibitor. Non-compartmental methods were employed to determine the pharmacokinetic parameters of ATX and its main active metabolite (glucuronidated form), 4-hydroxyatomoxetine-<i>O</i>-glucuronide. <b><i>Results:</i></b> The results revealed significant differences between the study periods for C_max, AUC_0-t and AUC_0-_∞ values corresponding to ATX and its metabolite. Small, but statistically significant increases in AUC values were reported for both parent drug (1,583.05 ± 1,040.29 vs. 2,111.55 ± 1,411.59 ng*h/ml) and 4-hydroxyatomoxetine-<i>O</i>-glucuronide (5,754.71 ± 1,235.5 vs. 6,293.17 ± 1,219.34 ng*h/ml) after combined treatment of ATX and the enzymatic inhibitor. <b><i>Conclusion:</i></b> FVX had a modest effect on the pharmacokinetics of ATX and 4-hydroxyatomoxetine-<i>O</i>-glucuronide. The presence or absence of any clinical consequences associated with this pharmacokinetic drug-drug interaction needs to be established in future studies.