It is estimated that 537 million people worldwide suffer from diabetes. According to the International Diabetes Foundation, this number is expected to increase to 643 million by 2030. With such a large population of patients, the market demand for new preparations that allow better tailoring of therapy to the individual needs of patients is growing. As part of the completed project, preliminary studies were conducted to develop technology for the extraction and methodology for assessing the quality of active substances of a natural origin with potential therapeutic significance in the treatment of insulin resistance. For this purpose, plant material with recognized supportive action in the treatment of insulin resistance was used—dried white mulberry leaves. Within the project, a methodology for qualitative studies was developed to verify the quality of the active substance extraction process. High-performance liquid chromatography (HPLC) with a C-18 column and ultraviolet (UV) optical detection was utilized for this purpose. The possibility of using two solvents for eluting active ingredients—acetonitrile and methanol—was tested, employing both isocratic and gradient programs. Optimal conditions for the extraction process were also determined. The experiments conducted allowed for the verification of the influence of the process duration (ranging from 0 to 180 minutes) and its environment (water, methanol, ethanol) on the efficiency of active substance extraction from plant material. The developed methodologies were used to determine which substances with potential hypoglycemic activity (based on literature reports) are present and can be effectively extracted from dried white mulberry leaves. For this purpose, mulberry leaves from different sources (two different producers) were used as the test material.