What Is Inositol?

"Inositol, sometimes called vitamin B8, is a sugar alcohol and structural isomer of glucose found in the cell membranes of all living organisms. It is involved in the production of membrane phospholipids, as well as being involved in the system which allows neurotransmitters to "talk" to cells and affect what happens inside them.

Inositol is used in the production of inositol triphosphate and diacylglycerol, both of which are molecules involved in the system that allows communication between neurotransmitters and the interior of cells. It is believed that a decrease in inositol could lead to a shortage of these two molecules, causing mood-regulating neurotransmitters -
such as serotonin, dopamineand norepinephrine - not to be able to properly communicate with the interior of brain cells. Supplementation with inositol could help depression by improving the functioning of this messenger system.

Is Inositol an Effective Treatment for Depression?

Thus far, inositol has mainly been investigated as an add-on to mood stabilizers and antidepressants for the treatment of the depressive symptoms of bipolar disorder."

Source
http://depression.about.com/od/Inositol/a/Inositol-For-Depression.htm