Dapoxetine hydrochloride is a selective serotonin reuptake inhibitor and the first drug approved for the on-demand treatment of premature ejaculation (PE). Our objective in this study was to characterize the efficacy of on-demand dapoxetine (30 and 60 mg) and daily paroxetine (20 mg) usage in treating PE. We conducted a 1 month study involving a total of 150 patients. Patients were divided into three groups of 50. Group 1 were treated with on-demand dapoxetine (30 mg), Group 2 with on-demand dapoxetine (60 mg) and Group 3 with daily paroxetine (20 mg). Our outcome measurement was increased from baseline intravaginal ejaculatory latency time (IELT) after treatment. The IELT increased from baseline to posttreatment by 117%, 117% and 170% in the paroxetine group (P < 0.01), 30 mg dapoxetine group (P < 0.01) and 60 mg dapoxetine group (P < 0.01), respectively. The increase from baseline IELT were similar for the 30 mg dapoxetine and paroxetine groups (P > 0.05), while the 60 mg dapoxetine group had a larger posttreatment IELT increase compared with the 30 mg dapoxetine (P < 0.05) and paroxetine (P < 0.01) groups. Dapoxetine (60 mg) 1-3 h before planned intercourse is a very effective treatment modality for PE. However, an on-demand dose of 30 mg dapoxetine is no more effective than the currently prescribed paroxetine treatment.