A method of delivering medicine by placing it in a special gel-like matrix that is applied to the skin. Each application will provide medicine for from one to several days. Nitroglycerin, fentanyl, lidocaine, estradiol, testosterone, and scopolamine may be administered through the skin. A transdermal drug patch has three key elements: a backing, the drug, and a liner that is peeled away before application. The absorption, delivery rate, and bio-distribution of the drug are not affected by the patient’s skin texture, thickness, or color. Drugs are equally well absorbed when applied to arms, thighs, back, or abdomen because various body sites have about the same rate of dermal penetration. When placed on intact skin, a transdermal drug patch creates a concentration gradient between the high concentration of drug in the patch and the low concentration in the skin. The drug then diffuses passively across the outermost skin layer (stratum corneum) into epidermal capillaries. Also called transdermal drug-delivery system.