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Aims: To estimate the effect of recreational legalization on cannabis use frequency and sources of variance across legal environments. Design: Longitudinal discordant twin and gene–environment interaction models in twins recruited from birth records and assessed prospectively. Setting: The United States, including states with different recreational cannabis policies before and after 2014, when recreational cannabis was first legalized. Participants: Two longitudinal, prospectively assessed samples of American twins aged 24–47 (n = 1425 in legal states, n = 1996 in illegal states), including 111 monozygotic pairs discordant for residence. Measurements Current cannabis use frequency (measured continuously and ordinally) was the primary outcome, and the predictor was recreational status of cannabis (legal/illegal) in the participant's state of residence at the time of assessment. Covariates include age, sex and cannabis use frequency prior to 2014. Findings Accounting for pre‐2014 use, residents of legal states used cannabis more frequently than residents of illegal states (b = 0.21, P = 8.08 × 10−5). Comparing 111 pairs of monozygotic twins discordant for residence confirmed the effect (b = 0.18, P = 0.014). There was inconclusive evidence for genetic influences on cannabis use frequency that were specific to the legal environment [χ2 = 2.9 × 10−9, degrees of freedom (d.f.) = 1, P > 0.999]. Existing genetic influences were moderated by the legal environment, as the genetic correlation between marijuana use before and after legalization was lower in states that legalized (rgenetic = 0.24) compared with states that did not (rgenetic = 0.78, Pdifference = 0.016). Conclusions: In the United States, there appears to be a ~ 20% average increase in cannabis use frequency attributable to recreational legalization, consistent across increasingly rigorous designs. In addition, the heritability of cannabis use frequency appears to be moderated by legalization. [ABSTRACT FROM AUTHOR]

Objective: Prior literature indicates that nontraditional attitudes are linked to higher intelligence. However, such attitudes in adolescence often accompany counter‐normative, delinquent‐type behaviors, which are themselves negatively linked with intelligence. This points to the possibility of suppression in the relationship between intelligence and nontraditional attitudes. Method: We analyzed a large community sample of 17 year olds (N = 3330) with data on intelligence, nontraditional attitudes, and a diverse collection of self‐ and teacher‐reported counter‐normative behaviors. Developmental questions for these relationships were examined through cross‐sectional comparisons between the adolescents and their parents as well as longitudinal analysis of the adolescent sample across emerging adulthood. Results: Youth who endorsed nontraditional attitudes had lower school grades, earlier age at first sex, heavier substance use, and were perceived as more oppositional by their teachers. Each of these problem behaviors was inversely related to intelligence. Accordingly, the positive correlation between nontraditional attitudes and intelligence was much weaker in adolescents as compared to their middle‐aged parents. Longitudinal analyses revealed that the association between nontraditional attitudes and intelligence strengthens in early adulthood. Conclusions: Associations between intelligence and sociopolitical attitudes can be obscured even by seemingly distal psychological characteristics. [ABSTRACT FROM AUTHOR]

Enhanced educational attainment and intelligence are consistent correlates of socially liberal, nontraditional attitudes. However, it is unclear how such associations unfold developmentally. Here, we propose an interaction effect between college exposure and intelligence on the development of nontraditional attitudes. Our rationale builds from the fact that a desired learning outcome of college education is to challenge traditional dogma and encourage diverse perspectives. Those with higher intellectual ability should be particularly adept at understanding the intended lesson and to show attendant increases in nontraditional attitudes. Data on social attitudes were obtained in a large community sample of youth at age 17 and remeasured at two points in early adulthood ( N = 2,769). Intelligence was linked with growth in nontraditional attitudes among those with higher educational attainment; no such association was observed among individuals who never attended college. Environments that encourage critical inquiry may thus steer brighter individuals toward the adoption of progressive worldviews., Competing Interests: Declaration of Conflicting InterestsThe author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.