Inositol is a six-carbon sugar alcohol and a naturally occurring isomer of glucose. Its importance for mental functioning is due to the key role that it plays in the phosphatidyl-inositol cycle. One of the two main ways that hormones and related molecules stimulate cellular activity is by acting on cell-surface receptors; then information arriving at the cell surface must be decoded into the internal messenger molecules (the "second messengers") responsible for transmitting messages into the cell. The phosphatidyl inositol cycle serves as a second messenger system for several of the noradrenalin, serotonin and cholinergic receptors, receptors that have important effects on brain function. It was found on autopsy that patients with affective disorders often had very low inositol levels in their brain. Abram Hoffer, MD commented years before that in general, if you are missing a nutrient for decades, you might need a much higher dose for the rest of your life to get back to normal.

Inositol is available from health food stores, should not be expensive and should be taken in powder form, because of the quantity needed to achieve clinical results. While it can be taken with or without food and is absorbed well, most doctors recommend it be taken with some food or juice. The amount found in the typical diet is approximately 1gm per day. This means it would be very difficult to achieve the levels needed by dietary means alone and supplementation is required.

The usual dose is 12 to 18gm per day. This dose usually must be taken for a minimum of three to four weeks in order to be effective. It may be taken as a single daily dose or in divided doses throughout the day. Feelings of well-being and reduced tension occurred at about six hours after a single dose.

Inositol does not seem to work with SSRI drugs synergistically. Using the two of them together is no better than using one or the other. Currently, it does not seem that a SSRI non-responder will see improvement with a inositol use.

The only side effect seen with inositol use has been loose stools in about one-quarter of those using it. As a very general recommendation, caution is advised for diabetics and anyone with severe kidney or liver disease.