T1-based methods typically measure and compare the T1 times of the free and bound ligands. A common way to measure the T1 value of a small molecule is the inversion recovery experiment [158,159], although other experiments are also available such as ultrafast NMR T1 [160] and saturation inversion recovery [161]. In general, the shorter T1 the relaxation time the less intense the peak signal will be and the broader the signal linewidth [162]. The T1 values of free and bound ligand will differ depending on how strongly the ligand binds because molecular interactions with the target will influence the ligand’s molecular motion, and hence, its longitudinal relaxation [156]. Bound ligands will have smaller T1 values than in their free form because, overall, they will experience slower molecular motion upon interacting with a target [163] therefore behaving like a much larger molecule. They can (depending on molecule size) also display a negative NOE difference spectrum (transferred NOE) [164], whereas non-binding ligands normally show small-positive NOEs [156]. For binding ligands to display negative NOEs, their T1 values must be comparatively longer than the 1/koff value of the target [156].