An innovative and comprehensive range of chromogenic reagents or colorimetric reagents are generally used for the application in the field of spectroscopic quantitative and qualitative analysis. There are number of reagents which are mostly utilized for the estimation of pharmaceutical medicinal agents. Functional groups generally present in medicinal drugs determine the way of analyzing them, because they are responsible for the properties of substances and estimate the identification reactions and the methods of quantitative determination of medicinal agents. Knowing the reactions for detecting functional groups, one can easily analyze any medicinal agents with complicated structure. This Reagents review provides information about the different reagents used in the estimation of the compounds by colorimetric methods. In this review reagent preparation, some reaction mechanisms, handling procedures and applications are discussed. This entire review covers the Bratton-Marshall (BM) [Diazotization followed by coupling], 3-Methyl-2-Benzothiazolinone Hydrazone Hydrochloride (MBTH) [oxidative coupling reaction], Para Dimethyl Amino Benzaldehyde (PDAB) and Para Dimethyl Amino Cinnamaldehye (PDAC) [condensation reactions with aromatic aldehydes], Folin-Ciocalteu (FC) [oxidation/reduction], 1,2-Naphtha Quinone-4-Sulphonate Sodium (NQS reagent), 2,6-Dichloro quinone-4-Chloroimide (Gibb's reagent), Bathophenanthroline, 1,10- phenanthroline, 2,2'-Bipyridine [oxidation followed by complex formation], METOL reagents [oxidation followed by charge transfer reaction]. In this review, we decorously summarized and discussed the important analytical chromogenic reagents regularly used in drug analysis by visible spectrophotometric methods. All above listed regents are most extensively used in the estimation of several pharmaceutical compounds. These reagents have a number of applications in the pharmaceutical field and also applied to novel analytical techniques.