Abstract: An occlusive body such as a patch, pad or bandage is provided which incorporates a reservoir (5) containing a physiologically active substance, the reservoir incorporating a membrane permeable to the active substance and either the membrane being hydrophilic and the reservoir contents being hydrophobic or vice-versa. The reservoir also contains a filler material such as methyl cellulose which immobilizes the reservoir contents by forming a gel. The dosage rate of the active substance through the membrane, when the latter is applied to the skin of a subject, is substantially constant until much of the dose has been delivered from the reservoir.