Alzheimer's disease is treated using THC (alone, or in combination with melatonin) administered in an ultra-low dose amount sufficient to (i) reduce A?? protein levels; (ii) reduce A?? aggregation: (iii) maintain A??PP protein levels; (iv) enhance mitochondrial functioning; (v) decrease phosphorylation of GSK-3?? protein; (vi) decrease GSK-3?? protein levels; (vii) decrease phosphorylation of Tau protein; and/or (viii) maintain Tau protein levels, in said patient without severe psychological impairments and side effects associated with higher doses of THC.Pharmaceuticals, Neuroscience, Medical