The present invention provides a method of treating or ameliorating a neurodegenerative disease in a mammal, the method comprising administering to the mammal a therapeutically effective amount of a neurodegenerative disease drug, wherein the drug is a substrate of an ABC transporter inhibitor, wherein the mammal is further administered a therapeutically effective amount of an ABC transporter inhibitor, whereby the neurodegenerative disease is treated in the mammal. In certain embodiments, the neurodegenerative disease comprises at least one selected from the group consisting of spinal cord injury, Alzheimer's disease, Parkinson's disease, Huntington's disease, prion disease, amyotrophic lateral sclerosis, a tauopathy, and chronic traumatic encephalopathy.