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Background: Only a small proportion of individuals who initiate nonmedical use of prescription opioids (NUPO) transition to heroin, suggesting that more nuanced aspects of NUPO may be better indicators of risk for escalating opioid use trajectories. This study leveraged panel data to identify NUPO typologies based on NUPO characteristics associated with opioid risk trajectories (route of administration, motives) and compared rates of heroin initiation at follow-up across typologies., Methods: Latent class analyses were run among respondents with no history of heroin use from the Monitoring the Future Panel Study (base year N=10,408) at modal ages 18, 19/20, 21/22, 23/24, and 25/26. Indicators included oral NUPO, nonoral NUPO, and NUPO motives to experiment, have a good time with friends, get high, escape problems, manage pain, relax, and sleep. Heroin initiation at follow-ups through modal age 29/30 was predicted from class membership., Results: No NUPO, self-medication (oral, manage pain), recreational (oral, nonoral, experiment, get high, have a good time with friends), and mixed-motive (all routes, all motives) classes emerged. Heroin initiation rates did not differ across no NUPO and self-medication classes; recreational and mixed-motives classes initiated heroin at higher rates than the other classes and comparable rates to each other. Non-NUPO drug use prior to heroin initiation was prevalent in recreational and mixed-motive classes., Conclusions: NUPO does not uniformly or uniquely increase risk for heroin initiation. Leveraging more nuanced indicators of risk for heroin use and targeting polysubstance use in addition to opioid-specific programming may enhance the efficacy of public health efforts., Competing Interests: Declaration of Competing Interest No conflict declared., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Background: Cannabis use patterns vary considerably, with many users reporting simultaneous and non-simultaneous use (co-use) of other substances. Despite this, little research has examined the extent to which subtypes of cannabis users may be identified based on their simultaneous and co-use behaviors., Methods: The sample consisted of adult Australian twins and siblings who reported lifetime cannabis use (n = 2590). A latent class analysis was conducted to determine subtypes of cannabis users based on five indicators of substance co-use and simultaneous use. Adolescent correlates (age of substance initiation and conduct disorder) and adult correlates (substance use/disorder and depression) of class membership were assessed. Twin similarity for class membership was also examined., Results: Four subtypes of users were identified: 1) alcohol co-users, 2) simultaneous alcohol users, 3) simultaneous tobacco users, and 4) simultaneous alcohol, tobacco, and drug users. Compared to co-users of alcohol, simultaneous alcohol users were at increased risk for alcohol problems. Patterns of use that involved simultaneous tobacco and cannabis use (i.e., simultaneous tobacco users and simultaneous alcohol, tobacco, and drug users) were associated with the most problematic outcomes, including substance use and disorder. There was evidence for genetic influences (12-58%) on cannabis use patterns, with higher concordance for latent class membership among monozygotic compared to dizygotic twins (χ 2 (1) = 7.19, p = 0.007)., Conclusions: The current study identified four classes of cannabis users at varying degrees of risk. Results suggest that simultaneous tobacco and cannabis use may be especially associated with deleterious outcomes., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Purpose: Using a genetically informed, discordant twin analysis, the objective of this study was to examine whether earlier onset of drinking and smoking behaviors predicted early sexual intercourse onset., Methods: Over 3,400 adult same-sex twins from the Australian Twin Registry completed a structured interview that included retrospective reports on onsets of smoking, drinking, intoxication, and sexual intercourse and conduct disorder symptoms. A two-level frailty model estimated within-twin-pair and between-twin-pair comparisons. Onsets of smoking, drinking, drunkenness, and conduct disorder symptoms were estimated as sexual intercourse onset predictors., Results: After controlling for conduct disorder, smoking and drinking onset did not predict sexual intercourse onset for either within-twin-pair or between-twin-pair comparisons. Drunkenness onset had a significant effect on sexual intercourse onset, such that twins who first experienced alcohol intoxication at a younger age than their co-twins were also more likely to have sex earlier than their co-twins., Conclusions: Relationships between substance use and sexual intercourse onsets may be due mostly to shared underlying factors; there was only a small relation between intoxication onset and sexual intercourse onset, and no direct relation between smoking and drinking onset and sexual intercourse onset., (Copyright © 2014 Society for Adolescent Health and Medicine. Published by Elsevier Inc. All rights reserved.)

Background: Risks associated with parental separation have received limited attention in research on children of parents with substance use disorders. We examined early substance involvement as a function of parental separation during childhood and parental alcohol and cannabis dependence., Method: Data were drawn from 1318 adolescent offspring of monozygotic (MZ) or dizygotic (DZ) Australian twin parents. Cox proportional hazards regression analyses were conducted predicting age at first use of alcohol, first alcohol intoxication, first use and first regular use of cigarettes, and first use of cannabis, from parental separation and both parent and cotwin substance dependence. Parent and cotwin alcohol and cannabis dependence were initially modeled separately, with post hoc tests for equality of effects., Results: With few exceptions, risks associated with parental alcohol versus cannabis dependence could be equated, with results largely suggestive of genetic transmission of risk from parental substance (alcohol or cannabis) dependence broadly defined. Controlling for parental substance dependence, parental separation was a strong predictor for all substance use variables, especially through age 13., Conclusion: Together, findings underscore the importance of parental separation as a risk-factor for early substance involvement over and above both genetic and environmental influences specific to parental alcohol and cannabis dependence., (Copyright © 2013 Elsevier Ireland Ltd. All rights reserved.)

In several national surveys a younger age of substance usage has been associated with a higher likelihood of the development of dependence. Some studies have suggested that age at first use is primarily an environmentally driven variable, whereas others suggest that it may be partially mediated by a general vulnerability to exhibit problem behaviors. Although Native Americans, overall, have the highest prevalence of substance dependence of any US ethnic group, the relationship of age of first marijuana use on the development of dependence in Native American populations is relatively unknown. Demographic information and DSM-III-R diagnoses were obtained from 525 Southwest California Indian adults residing on contiguous reservations. Multinomial logistic regression was used to investigate the relationship between age of first use and marijuana use disorders. Early marijuana use was found to be strongly associated with abuse and dependence in this population, even in the presence of several other risk factors including externalizing diagnoses. These data suggest that effective environmental prevention efforts at reducing early marijuana use may be an important strategy to lower the prevalence of use disorders in this high risk population.

Objective: To evaluate the equal environments assumption (EEA) of the twin method for mother-reported symptoms of child and adolescent emotional and behavioral problems., Method: Four emotional and behavioral problem scales (symptoms of separation anxiety disorder, attention-deficit/hyperactivity disorder, oppositional defiant disorder, and conduct disorder) and four environmental similarity measures (sharing friends, sharing classes, dressing alike, and perceived zygosity) were assessed by telephone interviews with the biological mothers of 1,948 female adolescent and young adult twin pairs. The effect of environmental similarity on the magnitude of the monozygotic and dizygotic twin correlations and on the parameter estimates from genetic model-fitting was examined for each symptom scale., Results: The measures of environmental similarity were not strongly or consistently related to the similarity of twins for mother-reported emotional and behavioral problems. On average, controlling for environmental similarity did not substantially affect estimates of genetic and environmental influences., Conclusions: These results lend support for the validity of the EEA and suggest that estimates of genetic and environmental influences obtained from twin studies of mother-reported child and adolescent emotional and behavioral problems are not unduly biased by the greater environmental similarity of monozygotic than dizygotic twins.