It is well known in industrial applications involving powders and granular materials that the presence of electrostatic charges influences drastically the material flowing properties. The triboelectric charges are produced during flow at the contacts between the grains and at the contacts between the grains and the container. Unfortunately, the triboelectric effect is still poorly understood, even at the fundamental level. Therefore, the approach to solve practical problems is mostly empirical. Moreover, reproducible electrostatic measurements are difficult to perform. In the present study, the ability of a set of excipients and active pharmaceutical ingredients (APIs) to produce electrostatic charges during flow in contact with different materials is analyzed with a recently developed instrument called GranuCharge. While different excipients have almost the same triboelectric behavior and a low chargability, APIs show complex triboelectric properties. Some APIs charge a lot while other APIs charge less. Afterward, the electrostatic behavior of API/excipient blends is considered. We show that the net charge of the blend is a complex function of the relative quantity of API in the mixture. Moreover, both the quantity and the sign of the charge are found to depend on the material in contact with the powder during the flow.