Do Differences in Learning Performance Precede or Follow Initiation of Marijuana Use?

Area of Science:

• Neuroscience
• Developmental Psychology
• Public Health

Background:

• Cross-sectional studies on age of marijuana initiation and memory deficits present conflicting results.
• Longitudinal data are limited, creating ongoing debate about whether memory issues stem from pre-existing conditions or are a consequence of early marijuana use.

Purpose of the Study:

• To investigate the longitudinal relationship between age at marijuana initiation and memory development.
• To determine if observed memory deficits are premorbid risk factors or sequelae of early marijuana use.

Main Methods:

• A community sample of 119 participants, predominantly African American, was followed from birth.
• Memory was assessed using four subtests of the Wide Range Assessment of Memory and Learning (WRAML/WRAML2) administered by masked examiners from childhood to young adulthood.
• Multivariable generalized estimating equation models analyzed longitudinal learning trajectories, categorizing participants into never users, later initiators (≥16 years), and earlier initiators (<16 years).

Main Results:

• No significant differences in childhood IQ or WRAML scores were found between marijuana initiation groups.
• In young adulthood, most WRAML2 subtest scores did not differ significantly between groups after controlling for sex and childhood IQ.
• Later initiators showed higher Story Memory scores in young adulthood and a more positive learning trajectory than never users, with earlier initiators exhibiting a decline in Story Memory post-adolescence.

Conclusions:

• Memory differences associated with earlier marijuana initiation may not be exclusively due to premorbid deficits.
• Findings suggest that marijuana use itself could influence cognitive trajectories, particularly in Story Memory, challenging the notion that observed deficits are solely pre-existing conditions.