A group of indolealkylamino-withasteroid conjugates, isolated and purified from Withania somnifera, are described. A synthetic method of making an indolealkylamino-withasteroid compound is provided. In vitro acetyl cholinesterase inhibitory activity and methods for treatment of dementia and dementia-related disorders, such as Alzheimer's disease, and anxiety and depressive disorders in mammals are demonstrated with these novel compositions.