Developmental transitions in the late adolescent to adult period
bring many environmental changes as well. Our study is one of only a
handful to address this important transition, allowing us to provide suggestive
hypotheses about whether the relationships between cigarettes,
marijuana, and depression remain stable even through these transitions.
The fact that the relationship between cigarette and marijuana
use diminishes over time is suggestive that one or both of these substances
are influenced by environmental features such as peers, family,
or maturation. Unlike the changing relationship between cigarette and
marijuana use during the adolescence–adult transition, relationships
between higher symptoms of depression and increased frequency of
marijuana use in males remained stable. Therefore, males with higher
symptoms of depression in adolescence have fewer changes in environment
or peer networks during the adolescence–adult transition. It is
also possible that their patterns of use may become entrenched in
adolescence, creating a negative feedback loop in which they use
marijuana to relieve symptoms of depression,which in turn contributes
to higher symptoms of depression via endogenous mechanisms (see
Chadwick, Miller, & Hurd, 2013) and environmental factors (isolation,
school or employment problems, etc.); and this pattern is difficult to
change in young adulthood for males.