The large-scale production of medicinal products is directly related to the presence of pharmaceutical drugs in sewage and water. The continuous input of medicines and its residues into the environment especially by sewage and wastewater generates an increasing need of new methods for its treatment and suitable control. The fluoxetine hydrochloride (FH), also known as Prozac??, is an active ingredient used in the treatment of depressive and anxiety disorders [1]. The present study focused on applying the ionizing radiation in order to reduce the acute toxicity of the FH drug solution, under its manipulated formula, to aquatic organisms. Hyalella azteca and Daphnia similis were the organisms used in the biological assays applied for the toxicity studies. It was used a Dynamitron electron beam accelerator and its energy was fixed at 1,4MeV for 5kGy and 10kGy doses [2]. For the calculation of the effective concentration (EC50) it was used the statistic program Trimmed Spearman - Karber. The average values for acute toxicity of FH were 0.59mg.L-1 (EC5 096h) for Hyalella azteca and of 1,44mg.L-1 (EC5 048h) for Daphnia similis. After irradiation of the FH aqueous solution, the following EC50 average values were obtained: 7.81mg.L-1 (5kGy) and 7.97mg.L-1 (10kGy) for Hyalella azteca; 8,46mg.L-1 (5kGy ) and 7.31mg.L-1 (10kGy ) for Daphnia similis. The obtained results revealed the FH as a very toxic compound. These results are confirmed by the EU - Directive 93/67/EEC (Commission of the European Communities) [3]. A significant reduction of the acute effects was obtained when 5kGy and 10kGy were applied.