Pharmaceuticals are continuously released into the aquatic environment mostly as waste water effluents through sewage treatment plants, run-offs, effluents from pharmaceutical manufacturing companies etc. This results in chronic exposure of aquatic organisms to these substances and their metabolites. Although, the concentrations of pharmaceuticals in the aquatic environment are usually in ngL-1 to g L-1 range, they are not likely to result in lethal toxicity. Nevertheless, extended and unabated exposure to low concentrations of drugs could lead to sublethal effects or even multigenerational effects. The aim of this study was to seek to improve the understanding of the effects of prolonged low-level exposure of Asellus aquaticus (aquatic macro-invertebrates) to mixtures of erythromycin, diclofenac and ibuprofen. On exposure to the mixture, growth rate decreased, feed intake was reduced but mortality was not significant for A. aquaticus. The effects of these pharmaceuticals on the growth, feeding and mortality of the test animal were as a result of the actions of the drugs and not attributed to a more general stress response. Although pharmaceuticals are indispensable to human health their usage and discharge to the aquatic environment coupled with their ecotoxicity to aquatic life may lead to ecological problems in the near future. Furthermore, this research confirms the suitability of the test species (A. aquaticus) as ecotoxicological test species that is both amenable to laboratory culture and sufficiently sensitive to provide reliable quantification of environmental risk.