Purpose: Pharmacological medications can reduce the radiation damage in the organism when applied in the stage before or after exposure to radiation. Cholinergic drugs are a category of pharmaceutical agents acting on the neurotransmitter acetylcholine, the primary neurotransmitter in the parasympathetic nervous system. In this investigation, some gamma radiation interaction parameters namely mass attenuation coefficients (mu(rho)), effective atomic number (Z(eff)) and electron densities (N-el) of 12 cholinergic system drugs have been calculated in the energy range 1 KeV-100 GeV. In addition, gamma-ray energy absorption (EABF) and exposure (EBF) of buildup factors have been computed using the five-parameter geometric progression (G-P) fitting formula for investigated drugs in the energy range 0.015-15 MeV, and for penetration depths up to 40 mean free path (mfp). Materials and methods: In order to perform these calculations, data obtained from WinXCom computer program were used. The computed mu(rho) values were then used to calculate the effective atomic numbers and electron density of the investigated drugs. To compute the buildup factors, the G-P fitting parameters were determined by the method of interpolation from the equivalent atomic number, 'Z(eq)' Results and Conclusions: It has been concluded that effective atomic number and electron density of malathion is bigger than the other drugs and the variations in values of Z(eff) and N-el for all drugs depend on chemical compositions and photon energy where the K-absorption edge of elements may affect the energy dependence of Z(eff) and N-el. It should also be noted that the buildup of photons is less in malathion and carbachol and is more in tabun and parathion compared with other drugs. Photon interaction parameters evaluated in the present study may be beneficial in radiation dosimetry and therapy.