Drug delivery systems (DDSs) are defined as formulations or devices that enable the introduction of a therapeutic substance in the body and improve its efficacy and safety by controlling the rate, time, and place of release of drugs in the body. This process includes the administration of the therapeutic product, the release of the active ingredients by the product, and the subsequent transport of the active ingredients across the biological membranes to the site of action. The term therapeutic substance also applies to an agent such as gene therapy that will induce in vivo production of the active therapeutic agent.

The scientific field dealing with this issue is known as drug delivery and has essentially the following aim: to deliver the drug at the right place, at the right concentration for the right period of time. When this is impossible by simply selecting an appropriate administration route, or if such administration causes patient discomfort, strategies based on the association of the drug with a carrier (a drug delivery system – DSS) are an alternative.

DSSs alter the biodistribution and pharmacokinetics of the associated drug: that is the time-dependent percentage of the administered dose in the different organs of the body. Furthermore, obstacles arising from low drug solubility, degradation (environmental or enzymatic), fast clearance rates, none-specific toxicity, inability to cross biological barriers, just to mention but a few may be addressed by DSS.

Drug delivery system is an interface between the patient and the drug. It may be a formulation of the drug to administer it for a therapeutic purpose or a device used to deliver the drug. The challenges of increasing the therapeutic effects of drugs, with a concurrent minimization of side effects, can be tackled through proper design and engineering of DSS, in a case-to-case manner.

If a device is introduced into the human body for purpose other than drug administration, such as therapeutic effect by a physical modality, or if a drug is incorporated into the device for preventing complications resulting from the device, it is regulated strictly as a device.