Abstract: The presented research aimed to develop microfluidic paper drug sensors (μPDSs). These hand-held devices offered decreased size, cost, and test ambiguity compared to available field drug tests. The sensors were modeled after Whitesides' microfluidic paper-based analytical devices (μPADs). Sensors 1.3-1.6 cm in diameter were: designed with SolidWorks engineering software, wax-printed onto chromatography paper, heated briefly at 150 °C to establish wax hydrophobic barriers, and treated at the sensor wells with colorimetric reagents. Iodoplatinate, cobalt thiocyanate, ferric chloride, and Fast Blue B reagents were used to test for caffeine, cocaine, morphine, and THC, respectively. Each reagent showed visible color change upon applying only microliters of drug solution. Sensors with multiple reagent wells permitted simultaneous analysis of a sample for several drugs. Test specificity was further improved by sensor image analysis. A weighted, red-green-blue histogram differentiated five false positives from the cocaine drug.