Methods and reagents are disclosed for conducting assays for EDDP. The reagents include a moiety selected from the group consisting of poly(amino acid) label moieties, non-poly(amino acid) label moieties, poly(amino acid) immunogenic carriers, non-poly(amino acid) immunogenic carriers, non-label poly(amino acid) moieties, and non-immunogenic carrier poly(amino acid) moieties linked to 2-ethylidene-1,5-dimethyl-3,3-diphenylpyrrolidine at the 3-position of one of the phenyl rings. Antibodies produced from immunogenic EDDP conjugates and labeled EDDP conjugates are employed in assays for determining the presence and/or amount of EDDP in samples suspected of containing EDDP.