Supercritical AntiSolvent precipitation (SAS) has been used to produce micronized particles of nalmefene hydrochloride, a selective narcotic antagonist and a promising adjunctive for the treatment of several kinds of addiction. Experiments have been performed using a laboratory scale apparatus and a semi-industrial scale plant. Ethyl alcohol (EtOH) has been used as liquid solvent because of its acceptability in processing pharmaceutical compounds. The effects of SAS process parameters such as temperature, pressure, at a constant concentration of the solute in the liquid solution (1.9 wt.%) have been studied. We have related the different powder morphologies obtained to the position of the process operating point with respect to the vapor-liquid equilibria (VLEs) of the ternary system nalmefene HCl/EtOH/CO2. Operating SAS well above the mixture critical point (MCP) of the mixture, nano-particles have been generated with a mean diameter ranging from 200 to 300 nm, near and below the MCP in the gas phase region, we have obtained submicro- and micro-particles with mean diameters ranging from 0.5 to 2 mu m. Balloons larger than 10-20 mu m in diameter and crystals have been also obtained. The results of interest obtained on the laboratory scale plant have been successfully reproduced on the semi-industrial scale plant. The micronized product has also been characterized using powder diffraction X-ray (XRD) and differential scanning calorimetry (DSC), to verify the influence of the micronization process on the final product properties. XRD analysis demonstrated that it is possible to obtain amorphous or crystalline precipitates, depending on the process conditions. (c) 2007 Elsevier B.V. All rights reserved.