Background: Relationships exist between perceived peer and own use of alcohol, cannabis, and tobacco, particularly when peers and participants are sex-matched. We investigated sex influences on social norms effects for college students' non-medical prescription drug use (NMPDU). Methods: N = 1986 college students reported on their perceptions of male and female peers' NMPDU frequency and their own past-month NMPDU. Results: Approximately 3% of students self-reported past month NMPDU, with no sex differences. In a linear mixed model, participants who engaged in NMPDU perceived significantly more frequent peer use. Female participants perceived more frequent peer NMPDU than did male participants, particularly when perceiving male peers' NMPDU. Significant positive correlations were found between perceived peer NMPDU frequency and participants' own NMPDU for all peer-participant sex combinations, with no evidence for stronger correlations with sex-matched pairs. Conclusions: While social norm interventions may be effective for college student NMPDU, sex-matching of these interventions is likely unnecessary.