Disclosed herein are compounds, extracts, and active fractions of the plant Geum japonicum and methods for preventing or treating brain diseases or conditions, such as ischemic stroke, Alzheimer's disease, vascular dementia, mild cognitive impairment (MCI), chronic cerebral ischemia and Parkinson's disease. The compounds provided herein can be formulated into pharmaceutical compositions and medicaments that are useful in the disclosed methods. Also provided are the use of the compounds and extracts in preparing pharmaceutical formulations and medicaments.