The object of the present invention is to provide a method for inhibiting the reduction of diphenhydramine in a pharmaceutical composition for external use. The pharmaceutical composition of the present invention contains diphenhydramine and/or its salt, and is contained in a container containing linear low-density polyethylene on the inner wall, and the carbon number of the side chain of the linear low-density polyethylene is 4 or less, can inhibit the reduction of diphenhydramine and/or its salt.本發明的目的在於提供一種用於抑制外用醫藥組成物中的苯海拉明類的減量的方法。本發明的醫藥組成物含有苯海拉明及/或其鹽，收容在內壁包含直鏈狀低密度聚乙烯的容器中，且所述直鏈狀低密度聚乙烯的側鏈的碳數為4以下，可抑制苯海拉明及/或其鹽的減量。
