We report here a patient with major depressive disorder who experienced severe adverse effects after the administration of SSRIs (serotonin selective reuptake inhibitors) without improvement of his depressive symptoms. These adverse effects disappeared and his depressive symptoms improved after discontinuation of the SSRIs and the administration of tianeptine. The patient exhibited a low value for the loudness dependent of auditory evoked potentials (LDAEP) -0.14 at baseline, which means that his central serotonergic neurotransmission was already highly active. We assumed that it was this high serotonergic activity that rendered him unresponsive to SSRIs, and brought on him the adverse effects, and that the tianeptine was effective due to the lack of serotonin reuptake inhibitory action. Thus, we suggest that LDAEP can be used to predict an individual patient's tolerability and clinical response to SSRIs in major depression.