A method of treating a neurodegenerative disease in a subject in need thereof comprises: (a) administering the subject an ornithine decarboxylase inhibitor such as alpha-difluoromethylornithine or a pharmaceutically acceptable salt or prodrug thereof in an amount effective to treat the disease; and concurrently (b) administering the subject a polyamine or a pharmaceutically acceptable salt or prodrug thereof in an amount effective to reduce damage to the gastroinestinal tract of the subject by the ornithine decarboxylase inhibitor.