A transdermal drug delivery system which enhances the delivery of the drug comprises a composition containing, as an enhancer, one or more C.sub.6 to C.sub.22 fatty acid esters of glycolic acid and its salts. These compositions are made up of a safe and effective amount of an active pharmaceutical permeant contained in a penetration-enhancing vehicle comprising, 0.25 to 50% w. of the fatty acid glycolic acid ester enhancer in a suitable carrier vehicle. These fatty acid glycolic acid ester enhancers may be used in various carrier vehicles to enhance the transdermal delivery of active permeants in either free form or used in an occlusive device, particularly in a transdermal patch in matrix or reservoir form. When used in matrix patch form, the fatty acid glycolic acid ester enhancers and permeants are incorporated into a biocompatible adhesive. When used in a reservoir type patch, the permeant and fatty acid glycolic acid ester enhancers are incorporated into a carrier fluid of controlled viscosity such as a gel or ointment preferably containing a lower alkanol and water. In free form, the enhancer and permeant may be incorporated into an ointment, lotion, cream, or similar formulation.