A peptide-based peroxidase inhibitor consisting of (a) the tripeptide having the formula AA 1 -AA 2 -AA 3, wherein AA 1 is a positively charged amino acid, AA 2 is a redox active aromatic amino acid, and AA 3 is an amino acid that comprises a thiol group and that possesses a reducing potential such that AA 3 is capable of undergoing a redox reaction with a radical of amino acid AA 2; (b) a retro or retro-inverso analog of the tripeptide of (a); or (c) a tripeptide of (a) or (b) further having a protecting group coupled to the amino terminus of the tripeptide, a protecting group coupled to the carboxyl terminus of the tripeptide, or protecting groups coupled to both the carboxyl terminus and amino terminus of the tripeptide, wherein the protecting groups are independently selected from the group consisting of acetyl, amide, 3 to 20 carbon alkyl groups, Fmoc, Tboc, 9-fluorene acetyl group, 1-fluorene carboxylic group, 9-florene carboxylic group, 9-fluorenone-1-carboxylic group, benzyloxycarbonyl, Xanthyl (Xan), Trityl (Trt), 4-methyltrityl (Mtt), 4-methoxytrityl (Mmt), 4-methoxy-2,3,6-trimethyl-benzenesulphonyl (Mtr), Mesitylene-2-sulphonyl (Mts), 4,4-dimethoxybenzhydryl (Mbh), Tosyl (Tos), 2,2,5,7,8-pentamethyl chroman-6-sulphonyl (Pmc), 4-methylbenzyl (MeBzl), 4-methoxybenzyl (MeOBzl), Benzyloxy (BzIO), Benzyl (Bzl), Benzoyl (Bz), 3-nitro-2-pyridinesulphenyl (Npys), 1-(4,4-dimethyl-2,6-dioxocyclohexylidene)ethyl (Dde), 2,6-dichlorobenzyl (2,6-DiCl-Bzl), 2-chlorobenzyloxycarbonyl (2-CI-Z), 2-bromobenzyloxycarbonyl (2-Br-Z), Benzyloxymethyl (Bom), t-butoxycarbonyl (Boc), cyclohexyloxy (cHxO), t-butoxymethyl (Bum), t-butoxy (tBuO), t-Butyl (tBu), Acetyl (Ac), and Trifluoroacetyl. (a) the tripeptide having the formula AA 1 -AA 2 -AA 3, wherein AA 1 is a positively charged amino acid, AA 2 is a redox active aromatic amino acid, and AA 3 is an amino acid that comprises a thiol group and that possesses a reducing potential such that AA 3 is capable of undergoing a redox reaction with a radical of amino acid AA 2; (b) a retro or retro-inverso analog of the tripeptide of (a); or (c) a tripeptide of (a) or (b) further having a protecting group coupled to the amino terminus of the tripeptide, a protecting group coupled to the carboxyl terminus of the tripeptide, or protecting groups coupled to both the carboxyl terminus and amino terminus of the tripeptide, wherein the protecting groups are independently selected from the group consisting of acetyl, amide, 3 to 20 carbon alkyl groups, Fmoc, Tboc, 9-fluorene acetyl group, 1-fluorene carboxylic group, 9-florene carboxylic group, 9-fluorenone-1-carboxylic group, benzyloxycarbonyl, Xanthyl (Xan), Trityl (Trt), 4-methyltrityl (Mtt), 4-methoxytrityl (Mmt), 4-methoxy-2,3,6-trimethyl-benzenesulphonyl (Mtr), Mesitylene-2-sulphonyl (Mts), 4,4-dimethoxybenzhydryl (Mbh), Tosyl (Tos), 2,2,5,7,8-pentamethyl chroman-6-sulphonyl (Pmc), 4-methylbenzyl (MeBzl), 4-methoxybenzyl (MeOBzl), Benzyloxy (BzIO), Benzyl (Bzl), Benzoyl (Bz), 3-nitro-2-pyridinesulphenyl (Npys), 1-(4,4-dimethyl-2,6-dioxocyclohexylidene)ethyl (Dde), 2,6-dichlorobenzyl (2,6-DiCl-Bzl), 2-chlorobenzyloxycarbonyl (2-CI-Z), 2-bromobenzyloxycarbonyl (2-Br-Z), Benzyloxymethyl (Bom), t-butoxycarbonyl (Boc), cyclohexyloxy (cHxO), t-butoxymethyl (Bum), t-butoxy (tBuO), t-Butyl (tBu), Acetyl (Ac), and Trifluoroacetyl.