The non-steroidal anti-inflammatory drug naproxen (NAP) has been coprecipitated with two different biopolymers, Eudragit (EUD) and poly(L-lactic acid) (PLA), by a supercritical antisolvent process (SAS). NAP release profiles were determined in simulated gastric and intestinal fluids in order to identify the best polymer to use for different administration routes. The in vitro release profiles of the NAP-EUD and NAP-PLA systems showed a slower and more controlled release in comparison to the untreated NAP. Moreover, the effects of pressure, temperature, initial concentration of the solution and drug-to-polymer ratio on the particle size and morphology of these drug-polymer systems have been evaluated. Although the morphology was spherical for both kinds of system, the NAP-PLA particles are larger than the NAP-EUD particles. A larger particle size is also obtained on using a lower pressure. However, the temperature did not influence, or only had a slight influence on, the particle size of NAP-PLA systems but it did have an influence on NAP-EUD systems. (C) 2014 Elsevier B.V. All rights reserved.