Transdermal drug delivery systems (TDDS) have always been a challenging area for research due to the barrier properties exhibited by the outermost layer of the skin's stratum corneum. The transdermal drug delivery system has been shown to be a reliable technology with considerable therapeutic advantages in comparison to all other dosage forms during the last two decades. Transdermal drug administration is able to maintain steady state blood concentration because it provides a regulated and predefined rate of drug release into the patient. When administering pharmacological compounds via the skin, morphological, biological, and physicochemical characteristics are taken into account for systemic effects. This approach offers a more regulated medication release and blood level profile than other dose forms, resulting in fewer side effects. It is a simple and painless procedure for patients. Transdermal drug delivery has made a substantial contribution to clinical practice; it has yet to reach its full potential as a substitute for oral drug delivery and hypodermic injections. The market for TDDS is expected to increase at a rapid pace in the next few years. This highlights the generations of transdermal drug administration in a new era of drug delivery. In this review, we discussed the many types of TDDS, their advantages and limitations, in-vitro and in-vivo investigations, development, and applications in a variety of disciplines

Transdermal drug delivery system (TDDS), mechanism of transport, iontophoresis, infusion mechanism, route of administration, microneedles.