Embodiments of the invention relate to methods for treatment of age-related cognitive decline in a patient comprising administering to the patient a low dose of tetrahydrocannabinol (THC), preferably in an amount of 10-400 micrograms (μg). THC may be administered in a variety of routes. Methods for delaying or slowing or reversing the progression of age-related cognitive decline using THC are also disclosed. The aforementioned methods may slow the progression of age-related cognitive decline. The cognitive decline may be in a patient suffering from Mild Cognitive Impairment (MCI) or a patient with no MCI, in which cognitive decline is prevented.