The invention disclosed herein relates to peptide inhibitors for transthyretin (TTR) aggregation and methods of inhibiting TTR aggregation, cytotoxicity, and/or TTR amyloidosis. Illustrative embodiments of the invention include a composition of matter comprising at least one peptide designed to inhibit the aggregation of TTR, with this peptide typically being coupled to a heterologous amino acid tag. A pharmaceutically acceptable carrier selected to be compatible with the inhibitory peptide may also be included. A method for blocking or inhibiting the aggregation of transthyretin TTR is also provided. The method comprises combining TTR with an effective amount of an inhibitory peptide or pharmaceutical composition, so that TTR aggregation and/or cytotoxicity is blocked or inhibited.