Objective: The prevalence of co-use of alcohol and cannabis is increasing, particularly among young adults. Sex differences in the effects of alcohol alone and cannabis alone have been observed in animals and humans. However, sex differences in the acute pharmacological effects of cannabis combined with alcohol have not yet been studied. In young adults, aged 19-29 years, we aimed to examine sex differences following an intoxicating dose of alcohol (target 0.08% breath alcohol content) combined with a moderate dose of cannabis (12.5% Δ⁹-tetrahydrocannabinol; THC) using an ad libitum smoking procedure. Method: Using a within-subjects design, 28 regular cannabis users (16 males; 12 females) received in random order: (a) placebo alcohol and placebo cannabis, (b) active alcohol and placebo cannabis, (c) placebo alcohol and active cannabis, and (d) active alcohol and active cannabis. Blood samples for THC were collected and measures of vital signs, subjective drug effects, and cognition were collected. Results: In the alcohol-cannabis combined condition, females smoked significantly less of the cannabis cigarette compared to males (p < .001), although both sexes smoked similar amounts in the other conditions. There was minimal evidence that females and males differed in THC blood concentrations, vitals, subjective effects, or cognitive measures. Conclusions: In the alcohol-cannabis combined condition, females experienced the same acute pharmacological and subjective effects of alcohol and cannabis as males, after smoking less cannabis, which has potential implications for informing education and policy. Further research is warranted on sex differences in cannabis pharmacology, as well as the combined effects of alcohol and cannabis. (PsycInfo Database Record (c) 2021 APA, all rights reserved).