Transdermal delivery system

A method of treating pain in a patient comprising applying a transdermal therapeutic system for transdermal administration of buprenorphine to the skin of said patient, wherein said transdermal therapeutic system comprises a buprenorphine-containing self-adhesive layer structure comprising

• A) a buprenorphine-impermeable backing layer, and
• B) a buprenorphine-containing pressure-sensitive adhesive layer on said buprenorphine-impermeable backing layer, said adhesive layer comprising
• a) at least one polymer-based pressure-sensitive adhesive based on polysiloxanes or polyisobutylenes,
• b) an analgesically effective amount of buprenorphine base or a pharmaceutically acceptable salt thereof,
• c) a viscosity-increasing substance in an amount of about 0.1% to about 8% of said buprenorphine-containing pressure-sensitive adhesive layer, and
• d) a carboxylic acid selected from the group consisting of oleic acid, linoleic acid, linolenic acid, levulinic acid and mixtures thereof, in an amount sufficient so that said analgesically effective amount of buprenorphine is solubilized therein to form a mixture including said viscosity-increasing substance, and wherein said carboxylic acid-, buprenorphine- and viscosity-increasing substance-containing mixture forms dispersed deposits in said pressure-sensitive adhesive, and
• wherein said buprenorphine-containing pressure-sensitive adhesive layer is the skin contact layer.