Structural properties and rotational dynamics of methyl groups in the most stable form of temazepam were investigated by means of ¹³C CP MAS NMR, quasielastic neutron scattering (QENS), and ¹H NMR spin–lattice relaxation methods. The QENS and ¹H NMR studies reveal the inequivalency of methyl groups, delivering their activation parameters. The structural properties of the system were explored in frame of periodic density functional theory (DFT) computations, giving insight into the reorientational barriers and providing understanding of the solid-state NMR results. The theoretical computations are shedding light on the intermolecular interactions along their relation with particular asymmetric structural units.