Sexual dysfunction, a common side effect of antipsychotic medications, may be partly caused by dopamine antagonism and elevation of prolactin. In QUALIFY, a randomized study, aripiprazole once-monthly 400 mg (AOM 400), a dopamine D2 receptor partial agonist, showed noninferiority and subsequent superiority versus paliperidone palmitate (PP), a dopamine D2 receptor antagonist, on the Heinrichs–Carpenter Quality-of-Life Scale (QLS) in patients with schizophrenia aged 18–60 years. Sexual dysfunction (Arizona Sexual Experience Scale) and serum prolactin levels were also assessed. Odds for sexual dysfunction were lower with AOM 400 versus PP [week 28 adjusted odds ratio (95% confidence interval), 0.29 (0.14–0.61); P=0.0012] in men [0.33 (0.13–0.86); P=0.023], women [0.14 (0.03–0.62); P=0.0099], and patients aged 18–35 years [0.04 (<0.01–0.34); P=0.003]. Among patients shifting from sexual dysfunction at baseline to none at week 28, there was a trend toward greater improvement in the QLS total score. The mean (SD) prolactin concentrations decreased with AOM 400 [−150.6 (274.4) mIU/l] and increased with PP [464.7 (867.5) mIU/l] in both men and women. Six PP-treated patients experienced prolactin-related adverse events. In addition to greater improvement on QLS, patients had a lower risk for sexual dysfunction and prolactin elevation with AOM 400 versus PP in QUALIFY.