This research was initiated as part of the fight against the public health problems of rising counterfeit, substandard, and poor quality medicines and herbal products in the Malaysian market. A simple, quick and cost-effective drug screening procedure using an incremental near infra-red [NIR] spectral database of common medicines in combination with principal component analysis [PCA] was developed to facilitate drug analysis without depending on standard compounds or products from manufacturers. The novelty of the approach is demonstrated by this two-tier method which allowed application in product identification, drug quality study, herbal analysis, and the detection of counterfeit and adulterated medicines. The NIR spectra database consisted of almost 4,000 spectra from 15 types of medicines and 3 types of herbal preparations, acquired and stored in the database throughout the study. The optimization procedure developed in this thesis on the database produced a search strategy using correlation and first derivative correlation algorithms on the full spectrum. The cut-off points of the hit quality index (HQI) were determined to classify the unknown sample in four categories; similar batch/match [classification type 1, 0.2). The same set of spectra were analysed by multivariate methods, including PCA. This two-tier screening approach proved successful when challenged firstly using simple compound drugs followed by complex mixtures of herbal preparations and then using alleged counterfeit and adulterated samples seized by the authority. The method developed has allowed samples to be identified without known background information which was difficult using other qualitative NIR techniques that required reference products for comparison. It is also allowed selection of suspected samples for further extensive analyses and in detection of adulterant contaminating herbal preparations. The outcomes of this thesis should support further qualitative and quantitative researches on drugs and herbals products in Malaysian universities. The developed spectral database of drugs will providea valuable tool to assist in drug quality surveillance nation-wide
