Undergraduate Honors Theses

Thesis Defended

Spring 2016

Document Type


Type of Thesis

Departmental Honors


Psychology & Neuroscience

First Advisor

Dr. Soo Rhee

Second Advisor

Dr. Richard Olson

Third Advisor

Tobin von der Nuell


Marijuana is one of the most widely used drugs in the United States, and the consequences of its use are mostly unknown. As marijuana becomes legalized and more widely available, it is important to investigate possible cognitive and mental health consequences of its use. The present study examined the associations between childhood internalizing behavior, adolescent marijuana use and early adulthood depression. A twin study was conducted to examine two alternative hypotheses regarding the association between adolescent marijuana use and early adulthood depression: 1. the association between marijuana use and depression is due to common genes or shared environmental influences, 2. after controlling for genetics and environmental factors on early internalizing behavior, the non-shared environmental factors that lead to marijuana use also lead to depression in adulthood (i.e., result more consistent with the causal hypothesis). There was a positive, statistically significant correlation between adolescent marijuana use and early adulthood depression, which was mostly explained by common shared environmental influences. There was little evidence that marijuana use has a causal influence on depression.