People suffering from depression often experience emotional and physical symptoms. Emotional symptoms can include sadness, loss of interest in things you once enjoyed, feelings of guilt or worthlessness, restlessness, and trouble concentrating or making decisions. Physical symptoms can include fatigue, vague aches and pains, headaches, and changes in weight or sleep patterns. For some, depression can include thoughts of death or suicide.

Researchers believe that depression is a result of an imbalance of naturally occurring chemicals (neurotransmitters) produced in our bodies called serotonin and norepinephrine (Meyers, 2000). These neurotransmitters, also known as "chemical messengers," help nerve cells communicate with one another by sending and receiving messages. These messengers are believed to regulate individuals' overall mood and pain receptors. Vaidya & Duman (2001) further explain that the regulation of intracellular messenger cascades exerts a powerful control on almost all aspects of neuronal function, inclusive of neuronal morphology, gene expression, activity, and survival. Those who experience depression are believed to have a low supply of chemical messengers, thus resulting in depressive symptoms. Meyers (2000) states that the synthesis of most neurotransmitters is controlled within the brain. For some neurotransmitters, the amount of biochemical precursors present in the brain can influence their rate of synthesis.