Provided herein are peptoids capable of inhibiting or reversing amyloid β (Aβ) fibril or plaque production. The peptoids form a helical structure with three monomers per helical turn and have at least four monomers with a side-chain having an arylalkyl or aryl group. The peptoid may be achiral. Also provided are methods of using the peptoids to inhibit or reverse aggregation of Aβ and methods of treating subjects with Alzheimer's disease (AD) or slowing the progression of AD.