ABSTRACT Objective To compare the efficacy and safety of amoxapine and vitamin B12 for treating retrograde ejaculation (RE). Materials and Methods Between May 2009 and November 2012, this open-label, randomized, crossover study enrolled 26 men suffering with RE at Department of Reproductive Medicine, Omori Hospital. Patients were randomly allocated into two groups (n=13 each). The amoxapine-B12 group received amoxapine (50 mg daily for 4 weeks, orally) followed (after a 1-week washout period) by vitamin B12 (500 μg three-times daily for 4 weeks). The B12-amoxapine group received the opposite regimen. All patients masturbated to ejaculation at least twice during each treatment period. The primary outcome was antegrade ejaculation of semen, as reported by the patient, on more than one occasion during either treatment period (defined as treatment success). Any adverse events were noted. Success rates were compared between treatments using Fisher’s exact test. Results One patient (B12-amoxapine group) withdrew for personal reasons (breakdown of marital relations); all other patients completed the study. Overall success rate was 88% (22/25). Success rate was higher for amoxapine than for vitamin B12 (80%, 20/25 vs 16%, 4/25; P<0.0001). 18 patients were responsive to amoxapine but not to vitamin B12, 2 patients were responsive to vitamin B12 but not amoxapine, 2 patients were responsive to both drugs, and 3 patients had no response to either drug. One patient (4%) reported sleepiness and 2 (8%) reported constipation while receiving amoxapine. No adverse events were reported during vitamin B12 treatment. Conclusions Amoxapine may be an effective, safe and well-tolerated therapy for RE.