Some drugs, used mainly in treatment of some neurological diseases and hypertension were exposed to gamma-irradiation, and the samples were investigated by electron paramagnetic resonance (EPR). The observed spectra were interpreted in terms of some type of alkyl and amine radical fragments. The spectra were computer simulated and the g values of the radicals and the hyperfine structure constants of the free electron with nearby protons were determined. The species were found to be stable at room temperature for more than a year. The samples were found to display no EPR signal without irradiation. (C) 2002 Elsevier Science Ltd. All rights reserved.