Tobacco, Cannabis, and Other Illicit Drug Use Among Finnish Adolescent Twins: Causal Relationship or Correlated Liabilities?

Abstract

ABSTRACT. Objective: Among Finnish adolescent twins, we compared (a) a model that describes a direct impact of liability to tobacco use on cannabis and other illicit drug use with (b) a model that included a shared underlying liability for these substances. Furthermore, the extent to which genetic and environmental infl uences contribute to the covariation between liabilities to use these substances was examined. Method: Tobacco and illicit drug use were assessed at age 17.5 years. Twin data on 3,744 individuals were analyzed using standard biometrical methods. Two alternative multivariate models were fi t and compared with Mx, a statistical program for genetic model fi tting. Results: The multivariate model, including a direct impact of the initiation of tobacco use on illicit drug use, provided the best fi t to the data. In this model, the total variation in the initiation of illicit drugs was decomposed to genetic factors (32%), common environmental factors (20%), unique environmental factors (8%), and a component due to initiation of smoking (40%). Most variation in the progression of illicit drug use was the result of initiation of smoking and illicit drug use (83%). Conclusions: Liability to initiate smoking directly affects illicit drug use in our best-fi tting model. Our fi ndings suggest that several common genetic infl uences may be related to tobacco use and illicit drugs but that a search for specifi c genes underlying illicit drug use is justifi ed as well. Such specifi c genes may hold a key to understanding biological vulnerabilities that lead to illicit drug use, which could aid in the development of targeted interventions. (J. Stud. Alcohol Drugs, 71, 5-14, 2010)

Cannabis and progression to other substance use in young adults: findings from a 13-year prospective population-based study

“…Our data on smoking uptake and cessation suggest a reciprocal relationship between cannabis use and cigarette smoking that varies according to age and stage of drug involvement,43 and which may be changing due to earlier initiation to cannabis use and decreasing approval of cigarette smoking. In addition to the mechanisms described above, our data on an increased likelihood of smoking among regular cannabis users may also reflect reduced barriers to smoking due to shared route of administration 43 44. Given the sparse literature on the natural history of cannabis and other drug use in young adulthood, a better understanding of possible mechanisms underpinning these associations is an important direction for research 45…”

Can the Gateway Hypothesis, the Common Liability Model and/or, the Route of Administration Model Predict Initiation of Cannabis Use During Adolescence? A Survival Analysis—The TRAILS Study

“…Perhaps as substance use progresses, the ROA becomes more important and therefore reinforces the type of substance used [30]. For instance, in a recently published study, Huizink et al [31] found that cannabis use might increase the risk (path coefficient of .32) of continued smoking behavior in an adolescent population. Therefore, the ROA may play a larger role in maintenance than in initiation of substance use.…”

A Molecular Basis for Nicotine as a Gateway Drug

“…Specifically, the use of tobacco or alcohol precedes the use of marijuana, which in turn precedes the use of cocaine and other illicit drugs. [1][2][3][4][5][6] Thus, in 2012, among U.S. adults 18 to 34 years of age who had ever used cocaine, 87.9% had smoked cigarettes before using cocaine, 5.7% began using cigarettes and cocaine at the same time, 3.5% used cocaine first, and 2.9% had never smoked cigarettes. Copyright © 2014 Massachusetts Medical Society.…”