The implicit membrane model IMM1 is extended to include the membrane dipole potential and applied to molecular dynamics simulations of the helical peptides alamethicin, WALP23, influenza hemagglutinin fusion peptide, HIV fusion peptide, magainin, and the pre-sequence of cytochrome c oxidase subunit IV (p25). The results show that the orientation of the peptides in the membrane can be influenced by the dipole potential. The binding affinity of all peptides except for the hemagglutinin fusion peptide decreases upon increase of the dipole potential. The changes in both orientation and binding affinity are explained by the interaction of the dipole potential with the helix backbone dipole and ionic side-chains. In general, peptides that tend to insert the N-terminus in the membrane and/or have positively charged side chains will lose binding affinity upon increase of the dipole potential.