An investigation based on an ultrasoft pseudopotential density functional theory (DFT) method, using the generalized gradient approximation (GGA) under periodic boundary conditions, has been performed in order to investigate how the presence of a neighboring dopant is affecting the CH 3 adsorption reaction (regarded to be an initial growth process). For this study, both the (100) and (111) diamond surface orientations have been considered, and various dopants in two different hydrogenated forms AH X (A = N, B, S, P, or C; X = 0 or 1 for S, X = 1 or 2 for N, B, and P, and X = 2 or 3 for C) were especially scrutinized. For most of the cases studied, the presence of a coadsorbed dopant was found to disfavor CH 3 adsorption with an efficiency that depends on the surface orientation as well as dopant type and position. The NH 2, PH 2, and SH species have the strongest effect in counteracting the CH 3 adsorption to the diamond (111) surface. This is also the situation with the dopants adsorbed on either of two specific surface sites (out of three positions studied) on the diamond (100)-2 x 1 surface. The main reasons for these observations are induced steric hindrances between the two coadsorbates. The BH 2 species, adsorbed to the third type of surface site on diamond (100), has been found to affect the adsorption reaction by formation of a C surf-B bond prior to CH 3 adsorption. The dopants in their radical forms are generally shown to always strongly disfavor the CH 3 adsorption reaction by formation of a C surf-X bond prior to adsorption. However, the NH radical will only form this new bond with the radical surface C site when it is adsorbed to position 3 on the surface.