Anthracene derivatives are class of the pharmacologically active natural compounds with laxative activity, and known to be the main constituents of senna and frangula. Within this study, knowledge on the medicinal properties of the Cassia and Frangula plants is enlarged by recent scientific reports on their phytochemical composition, in vitro and in vivo studies on the mechanisms of their activity and toxicity as well as the clinical proof of their efficiency. Comparative phytochemical analyses of senna- and frangula- containing medicinal products were performed according to appropriate European Pharmacopoeia monographs, with a goal to evaluate and compare the quality of all anthracen laxatives available on the Croatian market. Identification of studied herbal drugs and their preparations was based on detection of active sennosides and glucofrangulins. Special emphasis was given to determination of total anthracene derivatives contents, as the most important indicator of the herbal medicine quality and therapeutic effectiveness. All products registered as herbal drugs complied with prescribed requirements, while phytotherapeutics belonging to other regulatory categories showed a wide variation in anthracene derivatives content. Pharmacopoeial methods were also applied for quality control of multicomponent herbal preparations containing senna- or frangula-herbal drugs. Considerable differences in contents of marker compounds suggested that standardization of raw plant material and extracts may be necessary for quality assurance of herbal medicines and also for their effective and safety use. There is a need for development and implementation of new, modern and faster methods for identification and quantification of anthracene constituents, especially for analyses of polyherbal preparations. The results indicated the need for harmonisation and improvement of legislation in the field of herbal preparations, in order to protect the health of patients.