Transdermal patches present certain attributes that make the efficacy, safety, and quality of the product and must be controlled in the laboratory through analytical techniques to ensure the performance and safety of the transdermal delivery system (or TDS). Some of them correspond to tests that are common to other pharmaceutical forms. However, due to the particular characteristics of transdermal patches, there are specific procedures that apply to TDSs and that are described in internationally recognized regulations and pharmacopoeias.