Recently, the presence of illicit drugs in effluents from Wastewater Treatment Plants (WWTPs) and the aquatic environment has raised concern over their possible negative effects on aquatic organisms. In this study, therefore ecotoxicological data was retrieved through a literature survey and by using the software ECOSAR. Predicted No Effect Concentrations (PNEC) of five types of illicit drugs and their metabolites including 1. Cocaine (COC) and its metabolite Benzoylecgonine (BE), 2. Amphetamine (AMPH), 3. Methamphetamine (METH), 4. Cannabis ((delta 9 tetrahydrocannabinol (THC), 11-Nor-9-carboxy-delta-9-tetrahydrocannabinol (THC-CCOH)) and 5. 3,4-Methylenedioxymethamphetamine (MDMA) for species of three trophic levels in aquatic ecosystems derived. Predicted Environmental Concentrations (PEC) of above-mentioned drugs in twelve WWTPs’ influent and two effluents in Halland County have been measured by Swedish Toxicology Research Center (SWETOX co). Acute and chronic Risk Quotients (RQ) of the mixture of illicit drugs based upon two novel approaches calculated for the effluents of two WWTPs. Wastewater treatment plant in Ängstorp found with better removal efficiency of above- mentioned illicit drugs and the lower total RQs of (0.01<MRQ_acute<0.1; MRQ_chronic = 0.13) in comparison with that of Västra Stranden with the total RQs of (0.1<MRQ_acute <1; MRQ_chronic = 1.4). Although the RQ of WWTPs’ effluent was higher than 1 in Västra Stranden, there was no potential of risk on aquatic organisms in surface waters receiving that effluent. AMPH and Cannabis found as the most degradable substances through the WWTPs with (90-100%) of removal efficiency. Moreover, the results revealed that Cannabis (THC-COOH) was the most hazardous illicit drug on aquatic species in case of acute and chronic effects while, in terms of genotoxicology, a mixture of Cocaine metabolites found the most dangerous mixture of illicit drugs on zebrafish embryos.