Transdermal

Transdermal delivery is a method in which a substance is formulated to pass through intact skin into the bloodstream for a systemic effect, most often via an adhesive patch.

Ordinary topical products act on or near the skin surface; transdermal systems are engineered to overcome the skin barrier using penetration enhancers, controlled-release reservoirs, or specific carriers. Nicotine, fentanyl, and hormone patches are established examples. Because the skin bypasses the digestive tract and liver, transdermal delivery avoids first-pass metabolism and can provide steady blood levels over many hours. Achieving this requires demonstration through blood sampling, not just application to the skin.

Transdermal cannabinoid patches and gels are marketed, and a small number of studies have measured blood levels of cannabidiol after transdermal application in animals and people, with results that depend heavily on the formulation. The term is sometimes used loosely for products that are in fact ordinary topicals, so a transdermal claim should be supported by the manufacturer's pharmacokinetic data. Readers meet this term on patch labels and in formulation research; it describes a delivery goal, not a guarantee.