Alzheimer's disease is characterized by deposition of the amyloid β-peptide (Aβ) in brain tissue of affected individuals. In recent years, many potential lead structures have been suggested that can potentially be used for diagnosis and therapy. However, the mode of action of these compounds is so far not understood. Among these small molecules, the Non-Steroidal Anti-Inflammatory Drug (NSAID) sulindac sulfide received a lot of attention. In this manuscript, we characterize the interaction between the monomeric Aβ peptide and the NSAID sulindac sulfide. We find that sulindac sulfide efficiently depletes the pool of toxic oligomers by enhancing the rate of fibril formation In vitro, sulindac sulfide forms colloidal particles which catalyze the formation of fibrils. Aggregation is immediate, presumably by perturbing the supersaturated Aβ solution. We find that sulindac sulfide induced aggregates are structurally homogeneous. The C-terminal part of the peptide adopts β-sheet structure, whereas the N-terminus is disordered. The salt bridge between D23 and K28 is present, similar as in the wild type fibril structure. 13C-19F TEDOR experiments suggest that sulindac sulfide co-localizes with the Aβ peptide in the aggregate.