Transdermal drug delivery systems may be constructed of a number of layers, including:

1) an occlusive backing membrane to protect the system from environmental entry and from loss of drug from the system or moisture from the skin 2) Drug reservoir or matrix system; store and release the drug at the skin-site; 3) a release liner, which is removed before application and enables drug release; 4) an adhesive layer to maintain contact with the skin after application.