noun
hair restorer; hair growth tonic
Refers to a product or substance intended to stimulate hair growth or restore lost hair.
彼は薄毛が気になって、高い毛生え薬を買った。
Worried about his thinning hair, he bought an expensive hair restorer.
育毛剤 is a more common modern term for hair growth tonic, while 毛生え薬 is a straightforward compound that may sound slightly old-fashioned or literal.
Compound of 毛 (ke, 'hair'), 生え (hae, stem of 生える 'to grow'), and 薬 (kusuri, 'medicine'). The reading けはえぐすり follows standard rendaku for 薬.