A medical adhesive comprising a plaster layer containing the following ingredients, characterized in that the ingredient 2 is incorporated in a larger amount than the ingredient 5 and in an amount not less than 25% by weight relative to the total amount of the ingredients 1.about.5, and the plaster layer is a W/O type:1 a medicinal ingredient,2 a hydrophobic polymer having a glass transition temperature (Tg) of -65.degree. C. to 35.degree. C.3 a percutaneous absorption-promoting agent,4 water, and5 a hydrophilic polymer which is soluble or capable of swelling in water; anda medical adhesive which comprises a porous base layer in the plaster layer or in contact with the plaster layer, which enable stable release of the medicinal ingredient, the percutaneous absorption-promoting agents and so on and sustaining of the pharmacological effects over a long period.