Substances present in the body that are not produced nor expected to be present in the body are called xenobiotics. Accordingly, pharmaceuticals are xenobiotics for humans and animals. In last year's pharmaceutical consumption has been picking upward due to the increasing number of new illnesses and the number of people suffering from it. Pharmaceuticals include all medicines used in the human and veterinary medicine, and food supplements. Modern drugs are mostly small organic compounds that are lipophilic and moderately soluble in water. As all the pharmacologically active compounds sooner or later end in the environment (mostly in water), it is necessary to investigate their effect on it, since very small doses cause certain pharmacological and physiological effects. The influence of pharmaceuticals on the living world is possible to examine by toxicity tests. The aim of this paper is to determine the toxicity of widely applied pharmaceuticals, as well as real samples after treatment of wastewater with advanced oxidation processes. Examined pharmaceuticals are classified into three groups according to the mode of action: antibiotics (gentamicin), anthelmintics (ivermectin, closantel, mebendazole) and chemotherapeutic agents (hydroxychloroquine). Toxicity was tested by the standard DIN 38412 L34 method using Vibrio fischeri, luminscent bacterium, that is sensitive to organic pollutants. The toxigenic environment causes inhibition of luminescence, and by measuring its change, it obtains a link between inhibition of bacterial culture and toxicity of the pharmaceutical. The same growth trend of toxicity curves for all xenobiotics has been noticed. However, none of the tested xenobiotics has caused complete inhibition of bacterial culture. Of the standard xenobiotics solutions, gentamicin, then closantel and ivermectin showed the highest inhibition, while mebendazole was showen suitable for bacterial culture growth. Water samples of hydroxychloroquine after application of advanced oxidation processes showed very low toxicity. This indicates the possibility of applying such water treatment system in the real sector as well.