Cyproheptadine is an H1 antihistamine, that is often illegally added in dietary supplements to stimulate appetite and gain weight in children, currently banned for use in health supplements according to the provisions of Circular 10/2021-BYT. The method was using the Agilent Triple Quadrupole 6460 with fragments 288.1 → 96.1 and 288.1 → 191.2 selected for quantitative and qualitative. The separation was carried out on XBridge C18 column (100 mm × 2.1 mm, 3.5 µm) with a mobile phase consisting of acetonitrile and 0,1% formic acid. The analyte was extracted with methanol and cleaned up by d-SPE technique using a mixture of PSA and C18 powder. The recovery was in the range of 80-110%, the accuracy met the requirements of AOAC for method validation at spiked concentrations on three matrices of dietary supplements (granules, syrup, and powdered milk). Limits of detection and quantification were achieved at 0.08 mg/kg and 0.25 mg/kg with the syrup; 0.15 mg/kg and 0.50 mg/kg with granule and powdered milk samples. The method has been applied to analyze 30 samples and detected cyproheptadine in a syrup sample at 1.67 mg/dose of 10 mL. This method can be applied to analyzing cyproheptadine in dietary supplements on the market as well as developing for simultaneous determination of other adulterants with similar properties and effects in our next studies.