Types of marijuana users by longitudinal course.

Area of Science:

• Psychology
• Addiction Science
• Developmental Psychology

Background:

• Alcoholism and antisocial behavior taxonomies often use two-group classifications based on developmental course.
• Typologies for illicit drug users are less developed, necessitating a specific taxonomy for marijuana users.

Purpose of the Study:

• To propose and validate a developmental taxonomy of marijuana users.
• To classify marijuana users based on age of onset, chronicity, and persistence of use.

Main Methods:

• Cluster analysis of a community sample of 708 marijuana users followed from adolescence to age 34-35.
• Utilized Ward method with relocation, ANOVA, and logit analyses to define and describe user clusters.

Main Results:

• Identified four marijuana user clusters: early onset-heavy use, early onset-light use, mid onset-heavy use, and late onset-light use.
• Groups differed in marijuana/other drug involvement, sociodemographics, and lifestyle.
• Early onset did not predominantly lead to heavy marijuana use; peer delinquency and mental health were factors in heavy use development.

Conclusions:

• A two-type classification is insufficient for understanding marijuana user heterogeneity.
• Early marijuana onset alone does not predict problematic use or polydrug use.
• Motivation for use and dysfunctional behaviors are key to developing problematic drug use and dependence.