Biopolymers offer an alternative to synthetic polymers derived from petrochemicals. Polyhydroxyalkanoates (PHAs) are bio-polyesters with different side chains generated by various microorganisms through the fermentation of sugar or lipids and have the potential to be developed and targeted in global polymeric materials. PHAs can be altered chemically through several methods, such as hydroxylation, carboxylation, epoxidation, and grafting. Also, PHA-copolymers can be prepared by polymerization with two or more monomers such as hydroxybutyrate, hydroxyvalerate, hydroxyhexanoate, and hydroxybutyrate. Due to their versatile properties, PHAs and PHA-copolymers have multiple applications across industries such as drug delivery, medical implants, and tissue engineering. This review outlines the latest advancements in drug delivery systems utilizing PHAs and PHA-copolymers produced through microbial sources.