Antiviral compounds like rimantadine, amantadine, and their derivatives are effective combatants against diseases such as influenza and dyskinesia. Characterization of structure and dynamics of these molecules is essential for understanding their antiviral activity. Here we conducted solid-state 2H NMR relaxometry to elucidate the internal dynamics and structural restraints of these compounds in the solid state. Quadrupolar-echo based relaxometry experiments were performed on powdered samples of deuterated rimantadine and amantadine. Spectral lineshapes indicated that for rimantadine the major active mode of internal motion is methyl rotation about its 3-fold axis with no rotation about the C-C axis linked to the cage, while amantadine exhibits rotation about the molecular axis. Large order parameters (>0.8) calculated from the residual quadrupolar couplings indicate that off-axial dynamics are restricted. Spin-lattice (T1Z) and quadrupolar-order relaxation times (T1Q) were calculated at multiple temperatures for different orientations within the powder. Both the temperature dependence and angular dependence of T1Z and T1Q were fit using various analytical models including anisotropic rotational diffusion [1,2], axial diffusion, and discrete jumps. For rimantadine, the axial diffusion and jump models were unable to reproduce the temperature dependence of T1Z and T1Q, whereas the anisotropic rotational diffusion model including off-axial dynamics gave a good fit. Parameters quantifying the internal dynamics such as activation energy and diffusion constants were calculated and used to successfully predict the angular dependence of the relaxation times. Application of NMR relaxometry to these drugs in their virus-bound state within the membrane will allow one to determine how the structural and dynamical properties of the drug molecules as well as the channel environment are modulated by each other.