A drug-containing patch allows transdermal administration of a drug. The patch features a hydrophobic reservoir containing the drug, where the reservoir has a first surface and a second surface. A drug-impermeable backing overlies the first surface of the reservoir. A release sheet may overlie the second surface of the reservoir. The hydrophobic reservoir contains a drug and a hydrophobic matrix, where the hydrophobic matrix includes a hydrophobic filler in an amount which is effective to adsorb said drug; and a mixture of polyisobutylene and mineral oil. The hydrophobic matrix may contain hydrophobic colloidal silica as the hydrophobic filler.The hydrophobic reservoir layer may serve as a skin-contacting adhesive layer. Alternatively, a release-controlling adhesive layer may serve as the skin-contacting adhesive layer. The release-controlling adhesive layer may contain hydrophobic colloidal silica and a mixture of polyisobutylene and mineral oil.