Abstract The five active drug substances and two of the excipients present in Frenadol™, a cold medication, were separated. The active drug components dextromethorphan HBr monohydrate, ascorbic acid, caffeine, paracetamol and chlorpheniramine maleate were quantitatively assayed by a mixed ion pair LC method. The excipients separated were citric acid and maleic acid. The HPLC assay included dual-wavelength detection to simultaneously quantify the large concentration of paracetamol and the much lower concentration of chlorpheniramine and dextromethorphan. Both tetrabutylammonium hydrogen sulphate (TBA) and pentane sulphonic acid (PSA) were necessary for resolution of the seven compounds. The TBA was necessary to lessen peak tailing for dextromethorphan and chlorpheniramine, to retain ascorbic acid and to shorten assay time. The pentane sulphonic acid enhanced peak shape for dextromethorphan and chlorpheniramine. The assay of the active drug substances was validated for use in quality control applications. Validation studies demonstrated that the procedure was accurate, linear, precise, reproducible and rugged. The method conformed to both USP and EC validation guidelines.