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Climate change is predicted to have significant impacts on aquatic ecosystems. When combined with other stressors such as environmental contaminants, increasing temperatures will have serious consequences to the physiology and behavior of aquatic organisms. Pharmaceuticals such as antidepressants from wastewater treatment plants have been shown to modify the behavior of non-target aquatic species. We tested over 2000 snails (Physa gyrina) from a creek in Pennsylvania, USA for their righting behavior when exposed to different combinations of temperature (12°, 20°, and 25 °C) and antidepressant (venlafaxine and fluoxetine) concentration for one week or 48 hours. Snails exposed for one week righted significantly faster in warmer temperatures and in almost all concentrations of both antidepressants compared to controls. Snails exposed for 48 hours showed similar responses to warmer temperature as they did when exposed for one week, but only at the highest antidepressant concentrations did they right significantly faster than the controls. Exposure to venlafaxine at low concentration (1.56 µg/L) for 48 hours resulted in significant inhibition of righting, indicative of a non-monotonic dose response. We discuss the possible consequences of increased water temperature combined with antidepressant contamination on snail behavior as well as the possible physiological mechanisms of action explaining non-monotonic dose responses. [ABSTRACT FROM AUTHOR]