Contamination of freshwater ecosystems with nonprescription pharmaceuticals is an emerging concern. Pharmaceuticals consumed by humans are excreted into wastewater and can enter aquatic ecosystems after passing through water treatment facilities, as most systems are designed to remove only nutrients and pathogens. To quantify stream ecosystem response to these compounds, we measured the influence of four commonly used nonprescription pharmaceuticals (ibuprofen, acetaminophen, caffeine, and nicotine) on stream sediment respiration and nutrient uptake. Pharmaceuticals were added to stream sediment cultures with subsequent measurements of dissolved oxygen and nutrient concentrations. Four treatments for each pharmaceutical were assessed and treatments were based on published mean and maximum concentrations detected in US streams. Preliminary data show sediment respiration is reduced by acetaminophen, with concentrations as low as 5.1 µg/L, and ibuprofen, with concentrations as low as 0.1 µg/L (ANOVA, p<0.05). Nicotine and caffeine treatments both increased dissolved oxygen concentrations (ANOVA, p<0.05), suggesting stimulation of sediment macroinvertebrates. Phosphate uptake did not change with pharmaceutical treatment or increased respiration. In contrast, we measured variable nitrate uptake among treatments. Our data show nonprescription pharmaceuticals may influence stream ecosystem function even at low concentrations.