The nicotine patch is a transepidermal...

The nicotine patch is a transepidermal patch designed to deliver nicotine, the addictive substance in cigarettes, directly through the skin into the bloodstream. The patch contains a drug reservoir sandwiched between a nonpermeable back layer and a permeable adhesive layer that attaches to the skin. The drug leaches slowly out of the reservoir, releasing small amounts of the drug at a constant rate for up to 24 hours. (Illustration by Electronic Illustrators Group.)