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Directional reflectance (DR) enables to differentiate between real and fake Viagra®.DR indicates differences in chemical composition and physical parameters.DR points differences in original and fake drugs with identical chemical composition.The WHO estimates that up to 10% of drugs on the market may be counterfeit. In order to prevent intensification of the phenomenon of drug counterfeiting, the methods for distinguishing genuine medicines from fake ones need to be developed.The aim of this study was to try to develop simple, reproducible and inexpensive method for distinguishing between original and counterfeit medicines based on the measurement of directional reflectance.The directional reflectance of 6 original Viagra® tablets (Pfizer) and 24 (4 different batches) counterfeit tablets (imitating Viagra®) was examined in six spectral bands: from 0.9 to 1.1 μm, from 1.9 to 2.6 μm, from 3.0 to 4.0 μm, from 3.0 to 5.0 μm, from 4.0 to 5.0 μm, from 8.0 to 12.0 μm, and for two angles of incidence, 20° and 60°. Directional hemispherical reflectometer was applied to measure directional reflectance.Significant statistical differences between the directional reflectance of the original Viagra® and counterfeit tablets were registered. Any difference in the value of directional reflectance for any spectral band or angle of incidence identifies the drug as a fake one.The proposed method of directional reflectance analysis enables to differentiate between the real Viagra® and fake tablets. Directional reflectance analysis is a fast (measurement time under 5s), cheap and reproducible method which does not require expensive equipment or specialized laboratory staff.It also seems to be an effective method, however, the effectiveness will be assessed after the extension of research.