[en] It is shown that the reaction field induced in an atom by a strong magnetic field is of order Bα in atomic units (for magnetic field strength B and fine structure constant α). The reaction field causes a dipole-dipole interatomic potential energy to exist between a pair of atoms of order B^3/2α^7/2, such that B must be of order α^-7/3 for the interatomic energy to be of order one atomic unit. B of this order corresponds to a field strength of 1.66 x 10¹² G, which is within the regime of field strengths considered in recent studies of atoms and molecules in the presence of a strong magnetic field