Targeted drug delivery systems aim to increase the concentration of medication in specific tissues while reducing it in other tissues. This improves efficacy and reduces side effects. Targeted delivery can be achieved passively based on the body's natural response, or actively through surface modifications to direct the drug carrier. Examples of targeted delivery systems include nanoparticles, liposomes, micelles, and dendrimers which can be engineered with ligands to bind to specific cell types like tumors.