Alcohol and marijuana are two of the most widely used substances in the U.S, with rates of alcohol and marijuana co-use increasing in recent years. Despite this increase, little is known about the effects of alcohol and marijuana co-use patterns (e.g., simultaneous, concurrent) on intimate partner aggression (IPA) perpetration. The purpose of the current study was to examine differences in IPA among simultaneous and concurrent alcohol and marijuana use groups and an alcohol-only group. Participants were 496 individuals (57% identifying as a woman) recruited nationally in April 2020 via Qualtrics Research Services who reported being in a current relationship and recently consuming alcohol. Individuals completed an online survey that included demographics, measures of COVID-19 stress, alcohol and marijuana use, and physical and psychological IPA perpetration. Based on survey responses, individuals were categorized as belonging to the alcohol use only group (n = 300), the concurrent alcohol and marijuana use group (n = 129), or the regular simultaneous alcohol and marijuana use group (n = 67). Due to inclusion criteria, there was no marijuana use only group. Individuals with regular simultaneous or concurrent alcohol and marijuana co-use reported more frequent physical and psychological IPA perpetration compared to those who only used alcohol. Neither physical nor psychological IPA perpetration frequency differed between individuals who reported regular simultaneous versus concurrent alcohol and marijuana co-use. Results suggest that alcohol and marijuana co-use in general, and not the specific pattern of use, is associated with an increased likelihood of IPA perpetration.