Pharmacogenetics (PGt), the study of a gene's influence on patient response to a drug, shows strong potential for explaining issues with efficacy related to antidepressant medications. Each year, antidepressants are one of the most commonly prescribed medications due to the millions of Americans affected by depression. Importantly, it is recognized that there is wide interpatient variability in drug response to antidepressants caused by genetic mutations, which can alter the pharmacodynamic (PD) and pharmacokinetic (PK) properties of various drugs used to treat depression. Proteins that are mainly involved in how patients respond to medications include receptors, drug-targeted proteins, drug transport proteins and drug-metabolizing enzymes. Specifically in depression, variations in the serotonin reuptake transporter (SERT-1 or 5-HTT), N-acetyltransferase (NAT2), cytochrome P450 (CYP) 2C19, 2D6, and 1A2 can affect the outcomes of patients receiving certain antidepressant medications. Utilizing PGt can help prevent the trial and error in prescribing antidepressants and lead to better patient outcomes in the treatment of depression. Pharmacists can utilize genetic information to help primary care physicians choose drug regimens that are more likely to benefit their patients. Although advances are being made in this subject matter, some major efforts of future research will evaluate the efficacy of drug regimens and the dosing of drugs based on patient genetics.