The problem to be solved by the present invention is to provide a medicament which, although it is a non-ergot
dopamine agonist (DA), reduces the risk of drowsiness side effects and exhibits excellent therapeutic effects on neurodegenerative diseases such as Parkinson's
disease (PD). The present invention relates to a pharmaceutical composition for treating neurodegenerative diseases such as Parkinson's
disease, comprising 1-{[(4aR,6R,8aR)-2-amino-3-cyano-8-methyl-4,4a,5,6,7,8,8a,9-octahydrothieno[3,2-g]quinolin-6-yl]carbonyl}-3-[2-(dimethylamino)ethyl]-1-propylurea or a pharmaceutically acceptable salt thereof. The pharmaceutical composition is characterized by
oral administration at a daily
dose of 0.25 mg to 2 mg in terms of the
free form.