[3] Inhibition of inositol monophosphatase may be key in the action of lithium in treating bipolar disorder, specifically manic depression.

[4] The catalyzed reaction: This enzyme belongs to the family of hydrolases, specifically those acting on phosphoric monoester bonds.

Finally an activated water molecule acts a nucleophile and hydrolyzes the substrate, giving inositol and inorganic phosphate.

[8] Inositol monophosphatase plays an important role in maintaining intracellular levels of myo-inositol, a molecule that forms the structural basis of several secondary messengers in eukaryotic cells.

Inositol triphosphate is also a second messenger which activates receptors on the endoplasmic reticulum to release calcium ion stores into the cytoplasm,[3][10][11] creating a complex signaling system that can be involved in modulating fertilization, proliferation, contraction, cell metabolism, vesicle and fluid secretion, and information processing in neuronal cells.

[13] Inositol monophosphatase has historically been believed to be a direct target of lithium, the primary treatment for bipolar disorder.

[4][14] Scientific support for this hypothesis exists but is limited; the complete role of lithium and inositol monophosphatase in treating bipolar disorder or reducing myo-inositol levels is not well understood.

[16] Valproate, another mood-stabilizing drug given to bipolar disorder patients, has also been shown to mimic the effects of lithium on myo-inositol.