Marijuana use is common among U.S. college students. Liberalization of marijuana use policies is hypothesized to decrease social norms discouraging use, which protects against marijuana use. This may increase the importance of protective behavioral strategies (PBS) to reduce marijuana use harm. This study tested direct and moderated (by sex) program effects of an adapted version of the Marijuana eCHECKUPTO GO, a web-based marijuana use intervention providing university-specific personalized feedback (PF) with normative information and PBS to students attending a university in a state with legalized adult recreational marijuana. Participants were 298 heavy-using college students randomly assigned to receive Marijuana eCHECKUPTO GO or strategies for healthy stress management (HSM). General linear models (GLMs) tested direct program effects on proximal intervention targets, marijuana use, and use consequences. Multi-group GLMs then tested the moderating effect of sex on direct intervention effects. Marijuana eCHECKUPTO GO participants reported decreases in estimated use prevalence (i.e., descriptive norms), self-reported hours high per week, days high per week, periods high per week, and weeks high per month. Sex moderated intervention effects on the use of PBS such that females in the PF condition increased their use of PBS more than males. Results demonstrate preliminary support for the adapted Marijuana eCHECKUPTO GO in reducing marijuana use for "heavy college-aged users". Future research should test adapted Marijuana eCHECKUPTO GO sustained effects over time, and examine whether program effects on harm reduction manifest after sustained (e.g., booster) program implementation.