The increased likelihood of rVUS in women who reported cannabis use during adolescence, relative to their genetically identical but unexposed co-twins (i.e. MZ odds ratio significantly greater than 1.0), and the significant person-specific environmental correlation indicated that the relationship between these behaviors might extend beyond familial predispositions, including (a) direct or indirect pathways from adolescent cannabis use to rVUS or (b) unmeasured common factors that precede both the adolescent onset of cannabis use and rVUS. Prior studies have proposed that providers of illicit substances, such as older peers, might be critical to the strong associations between adolescent cannabis and other illicit drug use (34;35). Such peer affiliations may be related to precocious adoption of adult roles (36), particularly in girls. In our sample as well, women reporting rVUS were more likely to report greater current affiliations with drug-using male peers, including romantic partners (OR 1.79 [95% CI 1.47-2.18]; also associated with adolescent cannabis use, OR 4.54 [95% CI 3.73-5.53]). In addition, both rVUS and adolescent cannabis use were associated with a greater number of romantic partners, an earlier age at
