Abstract: Polyhydroxylated and dehydrogenated metabolites of 9-amino-1,2,3,4-tetrahydro-acridine (Tacrine) in which attached to at least two of the carbon atoms numbered 1,2,3 and 4 is a hydroxyl group and to the others either hydrogen, hydroxyl or double bonded oxygen the residual valencies being occupied by hydrogen or double bonds between carbon atoms 1 and 2 and/or 3 and 4 are disclosed as being useful medicaments for enhancing memory and cognitive function in Alzheimer's disease because they have retained the anticholinesterase activity of their metabolic precursor while circumventing its hepatotoxicity. Related compounds to which this disclosure also applies include those in which the aromatic ring is substituted with lower alkyl, lower alkoxy, halogen, hydroxy, nitro, trifluoromethyl, alkyl-N-substituted carboxamides and where the 9-amino group is mono or di-substituted independently.