Transdermal administration delivers medication through the skin via patches or other delivery systems.

They...

Avoid the first-pass effect of metabolism associated with the oral route and allows for improved bioavailability.

Prolong release of certain medications, which can improve patient adherence.

Minimize adverse effects due to lower drug peak concentrations.

THE DERMATOLOGY MARKET
2017 Market Size
2017-2020
2020 Market Size Estimate
Global Transdermal Delivery  Market Forecast
(In Billions of USD, LTS Gruppe, 2018)

Patches and gels are the two most prevalent TDDS for API while sprays and creams are more prevalent for OTC therapies. The most widely used APIs for TDDS are:

 

The Issues with Transdermal Patches and Delivery of Active Pharmaceutical Agents (APIs)