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Access Type

Open Access Thesis

Document Type


Degree Program

Public Health

Degree Type

Master of Science (M.S.)

Year Degree Awarded


Month Degree Awarded



Colorectal cancer is the third most common cancer among U.S. women; 63,610 new cases were estimated to have occurred in 2015. Prior studies found a reduced risk of colorectal cancer among antidepressant (AD) users, however, none adjusted for depression, which is itself linked to increased colorectal cancer risk and could confound this relationship. We assessed the relationship between ADs and AD drug classes with risk of colorectal cancer in a prospective cohort of 145,190 women between the ages of 50-79 without a previous history of cancer at enrollment. Current AD use was assessed at baseline. Over an average follow-up of 14 years, there were 5,280 incident cases of colorectal cancer cases. Cox proportional hazard ratios, adjusted for potential confounders including depressive symptoms, were used to estimate hazard ratios. Of all AD users, 51.1% used selective serotonin reuptake inhibitors (SSRIs), 40.7% used tricyclic antidepressants (TCAs), and 15.1% used other ADs. No association was observed between total AD use, SSRI use, and/or other ADs and risk of colorectal cancer. We observed a reduced risk of colorectal cancer among TCA users, which was significant for colon cancer specifically (HR 0.68, 95% CI: 0.48-0.96). Although a reduced risk of colon cancer was observed for TCAs use for less than two years (HR 0.39, 95%: CI 0.19-0.82), no association was observed for TCA use for two or more years (HR 0.85, 95%CI: 0.57-1.26). Our data suggests a protective association between TCA use and risk of colorectal cancer, however more research is needed to verify these findings.


First Advisor

Katherine W. Reeves

Second Advisor

Susan R. Sturgeon