Plants are widely used in many indigenous systems of medicine for therapeutic purposes and are increasingly becoming popular in modern society as alternatives to synthetic medicines. Bioactive principles are derived from the products of plant primary metabolites, which are associated with the process of photosynthesis. The present review highlighted the chemical diversity and medicinal potentials of bioactive principles as well inherent toxicity concerns associated with the use of these plant products, which are of relevance to the clinician, pharmacist or toxicologist. Plant materials are composed of vast array of bioactive principles of which their isolation, identification and characterization for analytical evaluation requires expertise with cutting edge analytical protocols and instrumentations. Bioactive principles are responsible for the therapeutic activities of medicinal plants and provide unlimited opportunities for new drug leads because of their unmatched availability and chemical diversity. For the most part, the beneficial or toxic outcomes of standardized plant extracts depend on the chemical peculiarities of the containing bioactive principles.