Abstract Objectives: In the Unani System of Medicine, the drugs having third- and fourth-degree temperaments are recommended to be prescribed after Islah (rectification/detoxification) to remove their toxins/minimize their harmful effects/enhance their efficacy. To validate the concept of islah-e-advia (rectification/detoxification of drugs), a fourth-degree drug, leaves of Mazaryun (Daphne oleoides Schreb.), has been selected in the present study to evaluate the changes if any in its chemical constituents before and after detoxification process through gas chromatography-mass spectroscopy (GC-MS) fingerprinting. Materials and Methods: The leaves of Mazaryun were detoxified by the method mentioned in Unani pharmacopeias. Then, comparative preliminary phytochemical and GC-MS analyses were carried out on aqueous extracts and powders of crude and detoxified samples of the test drug, respectively. The components revealed in GC-MS fingerprinting were identified as per the National Institute of Standards and Technology and Wiley Library using the m/z ratio. The identification of components was based on the retention time (Rt) values, molecular masses molecular formula, and peak area (percentages). Results: The phytochemical study showed the presence of saponins and triterpenoids in its detoxified form. The GC-MS fingerprinting revealed the existence of eight components in its crude sample with the molecular formula: C19H26N2S2; C16H32O2; C9H11N; C17H30O2; C16H28O2; C18H30O2; C28H38O19; and C16H48O6Si7. The detoxified sample evident the presence of eight different components, with the molecular formula: C18H26O4; C13H20O5; C15H24O9; C11H22NO4P; C36H66O3; C11H32O4Si4; C30H50O; and C30H50O, at different values, molecular masses, and percentages, respectively, out of which β-amyrin (C30H50O) and α-amyrin (C30H50O) were found in more percentage, 29.123% and 47.946%, at Rt 54.316 and 57.863, respectively. Conclusion: The presence of totally different components in crude and detoxified samples of test drug has validated the concept of islah-e-advia. β-amyrin and α-amyrin can be utilized as reference marker compounds to identify the detoxified leaves of Mazaryun for future researchers working on this drug.