Transdermal patch

A transdermal patch is an adhesive pad that holds a drug or active ingredient against the skin and releases it steadily into the bloodstream over hours or days.

The patch contains a reservoir or matrix of the active compound, a controlled-release layer and, often, penetration enhancers that help molecules cross the tough outer layer of skin. Because delivery is continuous, blood levels stay relatively flat, avoiding the peaks and troughs of oral servings, and the liver's first-pass metabolism is bypassed. Approved transdermal patches include nicotine, fentanyl, estrogen and motion-sickness medicines; each required proof that the compound actually reaches circulation.

Cannabinoid patches are sold as consumer products with claims of transdermal delivery, but cannabinoids are large and fat-soluble, and human data showing meaningful blood levels from a hemp patch are scarce. Many function more like a long-contact topical, acting locally rather than systemically. Patches differ from balms, creams and salves, which are not designed to deliver cannabinoids into the bloodstream.