Administration of drug delivery systems allows reaching therapeutic efficiency in comparison with traditional dosage forms. Microspheres are used quite often as drug delivery systems in pharmaceutical technology. There are a polymeric carrier and a drug substance in microspheres. Incorporation of a drug substance in a polymeric matrix (carrier) extends the drug release duration by half a year. There are several methods for obtaining microspheres. Depending on the physical and chemical properties drug substances incorporate either by the double emulsification methods or by the single emulsification methods. Naltrexone hydrochloride is a water-soluble drug substance. It has antagonistic activity with respect to opioid receptors. Naltrexone incorporates into microspheres in the form of a water/oil/water type emulsion. In this work the factors that influence the size of microspheres and incorporation efficiency of Naltrexone were studied: the concentration of poly(lactic-co-glycolic acid) copolymer (PLGA); the type of the stabilizer and its concentration; the volume of an external and internal phase; the type and speed of mechanical influence on a secondary emulsion. The method of double emulsification for drug delivery systems with modified release showed low efficiency: the efficiency of Naltrexone incorporation into microspheres didn't exceed 25%.