MAPT and Alzheimer disease: An important mechanism of lithium is that it inhibits certain enzymes in a noncompetitive manner by displacing the required divalent cation, magnesium.10 Klein and Melton identified glycogen synthase kinase 3β (GSK3β) as one such molecular target of lithium.11 In the context of AD, this enzyme phosphorylates tau at most serine and threonine residues in the paired helical filaments.