A drug is encapsulated within micron-sized polymeric carriers to enable a long-term and stable release of the drug at an effective concentration in the body to achieve the desired efficacy, thereby reducing the frequency need for medication administration. These polymeric carriers can be metabolized by the human body. The duration of the drug release is influenced by the ratio of the composition of the polymeric carrier and the modification method of the carrier. The technology is primarily used for injectable drugs, which requires an advanced level of technological capability and highly-controlled manufacturing processes.