<p>&nbsp;As it is known, antihypertensive drugs are frequently used for the treatment of individuals with high blood pressure</p><p>all over the world. This study aims is to precisely determine the active substances of telmisartan and hydrochlorothiazide, which</p><p>are commercially sold as high blood pressure drugs in the market, and to use the ratio spectrum method for this purpose.</p><p>Method: All, solutions of the active ingredients of the drugs studied in the method were prepared in various concentrations.</p><p>Subsequently, mixtures were prepared in accordance with the commercial drug sample, their spectra were taken by</p><p>spectrophotometric method, and the spectrum ratio method was successfully applied to these data sets.</p><p>Results: The study revealed that the application of the ratio spectra first-order derivative spectrophotometric method yielded</p><p>highly reliable outcomes in the spectrophotometric analysis of different combinations of telmisartan and hydrochlorothiazide.</p>