noun
A medicine that promotes bowel movements. The term is somewhat plain and direct; in medical or polite contexts, 下剤 (げざい) is more common.
See also: 下剤
便秘がひどいので、下し薬を飲んだ。
My constipation was severe, so I took a laxative.
More formal and medical term for laxative; 下し薬 is a plainer, everyday expression.
Compound of 下し (くだし, the continuative form of 下す 'to let go, to pass') + 薬 (くすり 'medicine').