In this study, radiation effect on an asthma drug Airfix and its ingredients (Montelukast sodium, Sorbitol) were analyzed by using EPR spectroscopy in the dose range of 10 Gy–30 kGy. The dependence of radiation-induced radicals on irradiation dose, temperature and time was investigated in detail. It has been determined that the radical observed predominantly in the Airfix structure originates from Sorbitol, and the characteristic features of this alkyl-type radical have been clearly defined using both experimental EPR and theoretical DFT methods. Dosimetric properties were investigated for all samples and it was suggested that Airfix drug and Sorbitol could be used as an EPR dosimeter through this radical agent which was determined to be very stable and sensitive to radiation. Moreover, it has been emphasized that other drugs containing Sorbitol excipient can also be used for dosimetric purposes in the dose range studied and even irradiation doses can be detected in case of radiation sterilization.