A significant investment in research has been conducted to define exposures andpotential hazards of pharmaceuticals in freshwater and terrestrial ecosystems. Incontrast, comparatively few empirical studies have been conducted forpharmaceuticals that are likely to enter coastal and marine ecosystems[1,2]. Theantidepressant venlafaxine (VLF) and some of its metabolites were recently foundin mussels caged in a coastal site receiving treated wastewater[3]. In those marineorganisms, very scarce data is available on the accumulation and/or metabolisationof pharmaceuticals. Consequently, it appears hazardous to conclude on the originof those metabolites in mussels, which could include a bioaccumulation throughdirect exposure as well as a metabolism of VLF in mussels. The aim of the presentwork was to quantify the accumulation of VLF in the marine mussel Mytilusgalloprovincialis and to evaluate the possible metabolism in laboratory controlledexperiments. The accumulation of VLF was evaluated in the whole mussel tissuesafter 1, 3 and 7 days of semi-static exposure by water (10µg L-1day-1) followedby 1, 3 and 7 days of depuration. Under those conditions, VLF attained an averagetissue concentration of (n=3) 2146.3 ± 156.0 ng g-1 dry weight (d.w.) in sevendays. The kinetic bioconcentration factor (BCF) was 265 ± 19 L kg-1 d.w. Sevendays of depuration allowed a decrease of tissue concentration to 21 ± 1.0 ng g-1d.w. Four VLF metabolites were quantified in mussel tissues and excreted inwater. The kinetics of those metabolites in water confirmed the metabolism ofVLF by mussels. Complementary experiment conducted at 1, 10 and 100 µL L-1nominal concentration clearly confirmed that M. galloprovincialis metabolizeVLF, with the quantification of studied metabolites excepted the NNO-VLF.These results gave a first approach on the ability of mussel to metabolizepharmaceuticals. Together with bioaccumulation information, this study provideda first approach on the pharmacokinetics of a pharmaceutical in a wild marinespecies, underlining the need of further experiments to better understand howvenlafaxine modulate the receptors in mussels and how exposure to thisantidepressant affects physiological functions of invertebrates.