The tolerability of dapoxetine, a short-acting selective serotonin reuptake inhibitor being developed for premature ejaculation, was evaluated when coadministered with tamsulosin. Adult men on a stable dose of tamsulosin were randomized to also receive dapoxetine 30 or 60 mg, or placebo, in a crossover design. Supine and standing vital signs were measured on days 1 and 7. Plasma samples were collected for measurement of tamsulosin, dapoxetine, and dapoxetine metabolites. Coadministration of dapoxetine with tamsulosin did not alter orthostatic profiles or affect the incidence of orthostatic hypotension. Tamsulosin and dapoxetine pharmacokinetics were not altered. Adverse events were reported by 5.4%, 10.9%, and 23.2% of participants receiving tamsulosin with placebo, dapoxetine 30 mg, and dapoxetine 60 mg, respectively. The most common adverse events were diarrhea, dizziness, headache, and nausea. Therefore, dapoxetine had no clinically important effects on the pharmacokinetics or ortho-static profile of tamsulosin in men on a stable tamsulosin regimen.