Tadalafil is a potent, selective, reversible phosphodiesterase 5 inhibitor under investigation for the treatment of erectile dysfunction (ED). Because some oral agents for ED have vasodilator properties, interaction studies were performed between tadalafil and commonly prescribed antihypertensive agents. In addition, cardiovascular safety assessments were made from a safety database of phase 3 studies comparing patients who were and who were not receiving antihypertensives. In patients receiving concomitant antihypertensive therapy, tadalafil administration may result in a reduction in blood pressure, which is, in general, mild and not likely to be of clinical concern. In the phase 3 studies, no statistically significant differences were observed between tadalafil and placebo in the mean changes in blood pressure from baseline in patients taking >or=2 antihypertensive agents. The incidence rates of cardiovascular events were comparable between patients who were and were not treated with concomitant antihypertensive therapy, with the exception of events recorded as hypertension, which would be expected to occur periodically in this patient population despite treatment. Hypotension or postural hypotension was not reported in any tadalafil-treated patient, compared with 1 report of each in the placebo-treated patients. Syncope was reported in 1 tadalafil-treated patient (0.1%) who was not on concomitant antihypertensive medication and in 2 patients (1.9%) who received placebo with concomitant antihypertensive agents. The data presented herein suggest that tadalafil is safe in patients receiving >or=1 concomitant antihypertensive agent.